This is a really neat mechanic, but, as mentioned, it's going to break a lot of ships. Overall, I like the idea, but I want to make sure that it's not like all-encompassingly terrible.
Heat needs to be regarded in a separate way as well, in my opinion:
Heat is the byproduct of
pushing a reactor past its limits. You don't generate any "heat" if your built-in cooling systems can take the heat (I'm a terrible
pun person, I know). But you start generating heat (Yes, this sounds a bit like IC2 from MC. I didn't even realize it til after I started writing) when your cooling systems can't keep up. So, yes, you have a set amount of power available to you "free", but when you start lobbing artillery rounds while your buddy is firing off the humongous autocannon as fast as he can, you're going to overrun your reactor's capabilities.....and stuff will go wrong from there.
Let's say at 10% heat it gets dangerous for NPCs (Or YOU) to be within the reactor's immediate area (Based on the bounding box proposed in the OP as the "heat area" or whatever)....because nobody likes a melted face. Or a melted ANY body part, for that matter.
Then at 25% heat "soft" blocks within the area start melting. Whenever we get means to resist solar heat, blocks that count as resistant would not take damage, but other blocks would start losing HP (And exploding, if anything functions like that after the update)
Say at 50% heat you start getting leakages in connected chambers. AKA, chambers connected to the reactor start dealing damage like the main reactor did at 25%.
At 75%, connected cooling devices start to lose HP.
If you're crazy, damaged, or dumb enough to push your ship into 90% heat, then you are taking extreme block damage from inside, and some small explosions can start going off.
If you reach 100% heat, well, say hello, reactor failure. I see two options here: We go for realism. Your ship becomes an irradiated wreck slowly burning itself away as the reactor continues to burn in a wildfire of nuclear/antimatter power that can't be stopped unless you get the reactor out of the ship. Option Two: the
Every Space Movie/TV Show/Game Ever Option. Screw realism! EVERYTHING EXPLODES. Good for keeping server databases clean!
Also, crew members DO NOT like watching their friends get burned to a crisp. So, maybe make sure the reactor techs are properly dressed and have a safe area, behind some closed doors and possibly engine-grade heat shields.
Obviously, all values and effects are just suggestions (Could that be why this is a discussion thread?!?!?!! ).
Power capacity doesn't need to be kept---weapons will use "power" (Which we do not actually need to see in any concrete sense. Abstract "power generated" out of the game and replace it, in build mode, with an indicator of "Heat [Percent Increase Per Second]") as it "charges" between shots. If you can't keep up, stop shooting the cannons til the missile's regenerated. Also, adds a lot of dynamics to combat this way. Adds choices. If you push your ship hard enough, maybe you get the lead to beat them...but if you can't keep it up long enough, stuff starts to melt...and you die.
As for shields using the same mechanic, I don't object to diversifying shields, perhaps even keeping some similar mechanics...but no blank repeats, please. If we're introducing variety, let's not immediately make anything else the same. A similar system, with a main shield system with
component parts that improve either regen or capacity would be a neat thing to do, but not as a clone of the proposed power system.