But still there should be a reason to keep conscripts alive at midgame and onřwards. I think that decreasing their reinforce cost once T3/T4 has been built will make them still useful as cannonfodder, reinforcing units and AT support.
I don't think that this could break the game balance, as conscripst's stats will keep being the same and their AI/AT capabilities so late in the game are not to be afraid even if spammed.
Bit of a contradiction there, saying you think they should have a reason to "be kept alive", but then you propose a cannonfodder role, which is pretty much exactly the opposite of keeping them alive...
They infact already fulfill that role due to 6man nature and a 1/3 lower per man reinforce cost than for example Grens. They carry a full two mens worth more soak, and each of them cheaper to replace.
Furthermore they already fulfill the reinforce units role throughout with Merge, and AT support with AT-Nade, especially with Oorah speed which makes it that much more possible to land the ordnance.
Therefore I dont see any actual justification, based on the reasons you give, for the change you propose.
Some people seem to operate off an assumption that Cons "should" scale to lategame, but are ignoring the fact that Cons actually carry their scaling capacity from the start. One means to demonstrate that, is imagine if Cons only got Oorah/Merge once you built T3/4. That would constitute scaling, but instead, as is, Cons already actually get this native advantage right from the start, at no additional cost.
Cons are fine.
Penals are the missing link.