I mostly read your post, may have missed some things due to how long it is, I will be sure to read through it properly and articulate my post more when I have the time.
I do agree that the movement needs to be fluid, currently when you hold a key down (I use sprint to dash) the character takes 2 steps and then pauses for less than a second. In my 400+ hours of playtime I've grown used to it, but I think a continuous movement like you suggested would be much better and allow for more control. I'd imagine that it would also make pulling off more complicated maneuvers easier.
If I recall correctly, the devs want to avoid artificial balancing as much as they can. One thing that could balance out light/heavy builds is that you make much less noise while moving around in lighter armor such as gambeson/leather as opposed to heavier armor such as plate, this could be very useful whenever stealth elements are added to the game. Right now if you don't want to be encumbered by wearing a full set of plate armor + chainmail + padding, you will need to invest in all 3 armor skills, there is only room for 5 total skills, so in the future the devs could add some new and interesting skills that would make players want to train those instead of mitigating encumbrance.
I don't really think armor is too advantageous if you have no encumbrance skills trained, you will be very slow to move, and your weapon swings will be slow unless it's a 2 handed weapon. There are also weapons such as the maul or polehammer that can defeat a full plated opponent with 2 well placed hits.
I agree with pretty much everything in your "General Combat Feedback" section besides feinting speed and a few other minor things. You can actually feint and even combo attacks really quickly if timed correctly, such as in this video (3:12). I've tried doing a fake overhead and then following up with a right-to-left swing and it's just as fast.
Everything in the "New Attacks" section would be great to see, especially running attacks and the Mordhau technique which I think will be in the game sooner or later, along with being able to use different pointy/blunt ends of other weapons such as polearms.
I'm not sure if the devs will go completely in depth with different stances and combat styles but I would love to see the character's general stance improve as more combat skills are trained.
I personally enjoy the current parrying/blocking system, I like having less keys to press which allows me to focus on combat more. I'm not sure how I feel about your suggestion, since it's well though out and does seem to expand on the combat and make it deeper, but it requires adding stuff to the HUD which I don't like, perhaps an exaggerated effect would be better but I'm not exactly sure.
Again, I'm not sure how I feel about the mouse changing when hovering over containers. On one hand it would make finding what to search less tedious, but on the other hand I actually enjoy being curios and clicking on everything that seems to be a drawer or a chest. However, I would love to see more drastic changes in the cursor to let you know you're out of range.
The entire inventory system will be getting a very big overhaul in the future, and I think it seems like an improvement and will be with-holding judgement until then. I see no harm in having the option to toggle between old and new.
Being able to move objects and bodies around easier would be a godsend.
Well, the dev tools in the Sui Generis alpha videos seems to be very user-friendly, although we haven't seen much of the engine yet. I think it's understandable that the devs aren't comfortable with giving out dev tools to everyone just yet, I think we will have to wait until at least Sui Generis is fully released. Modding could basically make the replay value of this game infinite. Hell, having just a custom dungeon maker would make the replay value infinite for me, but I think that's a little too much to expect from Exanima, especially since we're gonna be getting a fully fleshed out arena mode.
I think we would all love to have as many updates on the progress of Exanima as possible, but if the devs give insider forum access to everyone then I think they would be going back on their promise in the kickstarter (One of the perks was access to an insider forum).
Something like an Exanima/SG subreddit would be nice, and more accessible too, but I think such things should wait until Exanima is fully released or at least until the devs start promoting it more.