Idea is simple, when you research one item it will lock you out of other options. Now I can hear you asking "why would you do that?". This stems from how currently there's no drawback to getting research of any kind(hold on Mr x), so you may as well get anything and everything combined with how we have no hard counter system. I'm still against hard counters, but I think it might be a fun idea of sorts if this was used to kinda limit how many tree's a commander can go in, or add in research that's one or the other. For example you can either get buildings that start at 50% health or increase max health by 10-25%. Both of these things would be too convenient, but depending on comm play style and team make up I can see the benefits of going with either one. I think this is one of the reasons we can't quite have infantry(outside of no real code support) or building upgrades at the moment, is that you would just kinda end up with über soldiers or indestructible buildings. So think of this more for side grades where either one is good to have, but there's still an actual choice to be made because you can't have both. For limiting how many trees it's kinda obvious what it would effect and do, but I would think capping it at 2 trees outside of mandatory mechanical would be good. Obviously comms would kinda run out of things to research faster, but I don't particularly see it as a bad thing. You could also try it as first couple is free and there's a res cost for opening further research.