Thanks for actually taking the time to read over all my brainstorming. Megaposts like that can be pretty overwhelming and I've seen plenty of people take a glance and just give up. I put a lot of time into that post and your response left me with no regrets about doing that. I always hope that I get point-by-point responses, but I never actually expect it. Taking the time to respond also really helps everyone understand your vision for the game and lets us give more useful suggestions and feedback.
It can be difficult to have a proper discussion without first sharing the vision, as you say, otherwise we have people suggesting "hey, you could do A and B!" when I haven't told anyone about C, which is totally incompatible with those ideas ;p
Fortunately there's a playable prototype, but still a lot of information yet to share.
On targeting, I guess bots with weapons blown off would now try and ram you and may still pose some threat, whereas shooting their propulsion would make them into a slow moving turret.
I personally don't enjoy how called shots are done in most games as there is usually one best option anyways. I also get pretty lazy and I believe I would default to core targeting in most any situation. EM weapons can also be kind of disabling so this might fill that niche for players who want to run past most enemies instead of fight them. There might be a place for targeting, but it would most certainly be hard to balance.
I really like the EM disabling idea. Right now robots other than Cogmind only accumulate corruption from EM hits, and corruption has no effect on them until they reach 100% (and die). Would have to make sure that EM doesn't become too powerful, though, since it's also a way to outright destroy robots. (This is most noticeable in the late game, where if you've accumulated enough EM weapons you can destroy even a Behemoth in a few hits despite barely scratching its armor.) Maybe while all EM weapons retain the primary purpose of causing corruption, a secondary stat determines their likeliness to disable a component temporarily.
It's funny you mention the bad implementations of called shots. Reminds me of years ago when I was introducing Fallout 3 to a friend and I had built my character around head shots because it was really effective. After watching me play for about 5 minutes, he said: "Could you stop shooting everyone in the head?" Ha! The logical response would be to point out it's the most effective strategy, but I can see his point, it really wasn't all that interesting...
I started thinking about energy->matter because of a few situations where I got unlucky enough to have way more advanced power systems than anything else, but nothing to use them on. My mind went straight to energy hungry forcefields/shields, but those seem to have been intentionally left out. I think they could have a place in the game if they are brought in line to be just as strong and durable as the armors, but with less weight and an energy cost to compensate. As long as parts are still being blown off at the same pace as before, shields should give the player more choices with energy/weight management without upsetting flow or balance.
You may not have found them, but the 7DRL does have shields. They're implemented using a "damage conversion" mechanic, whereby they block damage by consuming energy at a certain energy to damage ratio. There are only four of them in the game though, so I guess you didn't come across any. As you bring it up, I've now added "powered armor" to the list of future parts, which could be implemented as a low-mass high-coverage armor that requires energy upkeep, like you suggest.
Snickered a bit as I imagined your sole remaining flight unit getting blown off as you fled across open lava 
Similar hilarity as I imagine you losing propulsion while on a conveyor that dumps you into lava.
That's even better!
Boostable: This is definitely worth considering, though it could make some builds potentially too fast.
For balance you might have to use the burnout options so that even if it makes you go that fast before the part broke.
Good idea, this should be able to make it in.
On Melee
Does speed affect certain weapons? Will ramming or attacking with a "spear" do more damage if I have 5 wheels or jet thrusters?
Currently the damage from melee attacks is purely weapon-dependent, and ramming is a random value from a range, but you're right speed should play a role in both. I'll increase the damage based on "momentum", which would refer to your speed and the number of consecutive moves in a straight line to the target. There will also be a small modifier even if you are immediately next to the target, but only if you meet some minimum speed requirement.
Piercing weapons should get a little extra bonus, too.
I'm glad to see the game doing so well on Screenshot Saturday!
I was pretty surprised at the amazing response that first weekend. Even this weekend it's done fairly well. I guess people are craving something that is quite obviously "different" from the rest.
(After today I'll be out of town with spotty Internet access until mid-November, so don't be surprised if I don't reply to anything for while.)