Repair currently costs 50% of the repaired unit's energy cost and none of its metal cost. It has been proposed to make repair cost some amount of metal and energy (current thinking is somewhere between 10% and 25% of both metal and energy).
Some comments on this idea:
- Since energy impacts overdrive, the current energy-only repair deprives you of a meaningful amount of metal in the early-mid game but becomes mostly negligible in the late-game. (If repair costs 10% metal and energy, you probably need energy income on the order of a singu for this to be worse for your metal income than 50% energy.)
- Chip damage from artillery in the lategame having a metal cost concerns me. Units like Tremor and Bertha don't seem like they need a lategame buff, and even if they are nerfed their role will remain problematic unless they are flat-out owled.
- Shields will still allow you to absorb damage at a purely-energy cost in the lategame.
- Metal-repair makes non-fatal damage to heavy lategame units like Paladin/Cyclops/Grizzly more impactful. I don't think the current state of Paladin is bad but I'm aware other people disagree with this assessment.
- At the moment, (as long as you aren't stalling energy) repair is effectively always high-priority since it causes you to have less overdrive income
to be shared among your other tasks. A repair which consumes metal would not have this property, for better or for worse.
- This change would presumably be accompanied by adding metal cost to resurrection, at either the same or higher resource cost. Rez could be made to cost metal even if repair is not. This particularly affects FFA in which resurrection is prevalent, and (afaik) generally felt to be overpowered.