Primaris SM Sketch

An interpretation of what the prototype of the primaris armor would have looked like.
I literally drew this right after the reveal video from Warhammer TV came out, but I haven't got to posting it until now because general procrastination. 
I watched the video and read the comments, and they bring up a valid point. If the Primaris marines wear mark 10 "Tacticus" armor, then what in the Emperor's friggin name happened to Mark 9!?!?! My thoughts are that the mark 9 armor was a prototype of the later Tacticus armor, but it aimed to perfect every single flaw in the history of Astartes power armor that the enhancements and upgrades were produced using mastercrafted Martian Artificer-wrought means which simply would be too expensive to produce at anywhere near the legion-numbers that Guilliman needs for his Indomitus crusade. 
When I saw the leaked images, I immediately picked up on a few things where the armor could have been reinforced, and so here is my interpretation of the planned upgrades into Mark 9 armor that were ultimately cut.
1.) Power field vambraces: Considering the Mark 8 armor had larger, more "powerfist-like" armplates and gauntlets, I thought that Cawl would use his Martian knowledge and access to potent technologies and improve upon the power of the armor by incorporating the technologies of a powerfist and thunder hammer into the vambrace of the armor in a smaller, more utilitarian package. This would eschew the need for waiting until more powerfist units were manufactured, using the designs for the smaller ones that the officers of the Imperial Guard use as a stopgap design. This would effectively allow the Primaris marines to do a ground pound unaugmented by powered weapons, when the need arises.
2.) Knee Ball-joints: Next is the implementation of an armored ball joint where the plates stop. This would allow for increased protection of the joints whilst not impeding the marine's movement. It could also be used to cover a sort of auxiliary exoskeletal support frame, allowing the marine to carry more equipment on him.
3.) Additional crotch Armor: more of a "why the hell not" move than anything else, the added plate here serves to cover the exposed undersuit which connects the crotch and leg armorplates. Considering a well placed shell or sniper shot at the normally exposed flexible parts of the armor would moderately to severely impair the marine's movement, the addition of an armored piece here would definitely help. 
4.) Alternative Waist Armor: Sure, the official mark 10 armor already has plates like these, but I thought that they were not enough as they did still left some of the waist joints exposed and unarmored. Additionally the sides of the marine's abdominal section look to be completely unarmored, a disconcerting thought to any Astartes potentially surrounded and being fired apon from multiple sides by the enemies of the Emperor. To combat this, I first added a layer of segmented armor to the exposed sections, like normal mark 7 armor except it can bend to a degree. The next thing to be implemented would be the improved Waist plates, since they also extend up towards the sides of the armor as well as covering the exposed leg joints. Added a ball-joint for extra maneuverability and sturdiness.
5.) Extended Elbowguard: An extended armoring of the elbow joint, which is an improvement wrought from the days of the late Heresy, when the Legionnes Astartes wore larger elbow plates. Might have gotten carried away, but the alternative design is segmented, as to not interfere with the function of the pauldrons. The extension also contains a smaller, conventional Mark 7 elbowguard beneath it for extra measure. Also helps to cover some of the powerfeed cabling to the powered vambraces.
6.) Elbow Ball Joint: Main function is to protect the sides of a marine;s elbow, which the conventional elbow joint would only halfway protect. Also serves to protect some of the powerfeed cabling to the powered vambraces. The armor only covers the sides of the arms, so movement is not impeded.
7.) Raised Gorget: The Mark 10 armor has an armored gorget, yes, but to me it seemed a bit short. The prototype would have had a raised gorget, providing a greater degree of protection for the marine, and making the neck-trap problem impossible to exploit. The gorget would be made of a reactive crystalflex alloy dating back to the Horus Heresy, the same stuff warship armorglass windows are made of and the same material that could be designed to be one-way see-through, so the enemy cannot distinguish the glass from armor, though in all fairness the crystalflex would be on par with Adamantium if it was left unreinforced on warships. The marine would be able to see, but his enemies not as much through.
8.) Layered Leg joints: I thought of the new leg armor for the primaris marines, and it has the same "issue" I think as the mark 6 Corvus armor, that being a static raised plate for the lower leg instead of covering it with a conventional kneeguard. My interpretation would have the armor incorporate both, the large and static armored leg in front, and a conventional kneeguard under it to compensate for armor protection if the marine is moving in a way which would leave his knees otherwise unprotected.
9.) Reactive Backpack Units: The prototype armor would've had an MIU link between the marine and the armor's systems, including the backpack. This would have allowed the marine to grab new clips, blades, and other miscellaneous tool needed from his backpack with but a thought, at least the equipment that was not already built into the armor. Generally would have made utility in the field easier.
10.) Omnispex Unit: An advanced multi-use augur and sensorium package coupled with the armor's auto senses which would allow the Primaris marine a superior degree of battlefield and communications awareness. Includes a backpack-mounted sensor cluster which can shift location on a magnetic tread on the backpack (built on Mars from the same technology used on Deathwatch armor), and a built-in rotating unit to compensate using the armor's machine spirit. The upper unit contains a crystalflex shield which is extra-reinforced against EMP and trice-consecrated by the Mechanicus against Chaos scrapcode and infection. Includes warp-sensors and emergency backup manifold systems.
11.) Backpack Thrusters: An assortment of small thrusters situated on the backpack unit of the marine's armor, whose main function is to allow for the marine to jump exponentially-higher distances than normally possible, evade fire and charge faster, and provide a greater degree of maneuverability and omnidirectional control in 0-gravity combat. Not nearly as bulky as the conventional jump pack.
12.) Pauldron Reinforcement: The Mark 9 armor would be reinforced by the molecular bonding studs so ubiquitous amongst the hodgepodge amalgamations of ancient Astartes plate that were the Mark 5 armors, a simple (though some would say crude) but nonetheless effective method of increasing the pauldron's impact resistance and durability, mainly on the pauldron used for charging, and the one used most often to face the enemy. The other pauldron is reinforced to a lesser degree with these studs, due to the need to maintain the place where the chapter's insignia is presented. To equalize the protection rating of both sides of the armor, the insignia pauldron's surface plate is somewhat thicker.

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