Why is Rapid Conscription bad?
It comes late, the best possible pay-off (480 mp) is not very high and scenarios where you can use it to full extent are hard to come by.
I had a proposal once that Rapid Conscription and Relief Infantry would grant 'reinforcement squads' that could not be reinforced, had crew weapons, and their only ability was Merge. The idea was they were strictly for field reinforcement, you would just merge them back into units until the squad was gone. That could still work for the Germans.
Yes, I remember discussing that solution too. At first I thought it was a sound idea, but in the end it's just a very roundabout way of doing Recoup Losses where you can only spend the extra MP on infantry. I think overall adding a new squad into the game for just that purpose is not worth it, so in my opinion Relief Infantry can just become Recoup Losses (with a name change and the "crawlers" fix, so it respectively makes more sense and triggers consistently).
I do think a big problem of Rapid Conscription / Relief Infantry is that you don't want to add new Vet0 Conscript or Osttruppen squads in later game stages. The mechanic of the game is to keep vetted troops alive and add in more powerful higher tech units. So this ability gets rapidly weaker with time.
So just a quick thought I had as I was reading this: While ability is active you get a chunck of manpower for each soldier dying. Easy to implement at both factions and a real helpful ability if you are still playing with mass infantry / team weapons in the late game and your opponent is bleeding you out. You are swapping munition for manpower in the end. You can cap manpower you get at some point of course.
The main idea behind this rework was that you can get those replacement squads
when you need them, not just when the ability is active.
No matter how good a player is, they are going to lose units. Thing is, you can't tell when it's going to happen, because as you said and as the game is designed - unit preservation is key. In live version of Rapid Conscription, you get replacement squads immediately when the ability is active. It's highly likely that you won't need those squads at that very moment, so you have a choice of either keeping them around (taking up your population and lowering your income) or, in case of Conscripts, merge them completely into existing squads to save MP.
In this rework version, you activate Rapid Conscription and gain a couple of squads in reserve while you're fighting and losing models as usual. You can call those squads immediately, just like in live to merge them into your troops and save some MP. Here's the important part though - those reserve squads can be kept in reserve indefinitely, so when you lose a squad further on during the match, you can immediately get a replacement for which you paid beforehand in Munitions (and model losses, but infantry squads will always lose models). Fresh Conscripts in late game aren't anyone's first choice, with 7-man squad they gain experience faster and can always be used to top-off veteran squads and weapon teams.
Plus, in live version, any lost models below 6 are lost between ability activations, but in this rework they are kept in the bank for next time.