In any case splitter ships render the slot limit useless except for cases where the individual ships can't be packed in a 102x102 grid. A multiplier wouldn't make splitters a thing of the past. One of mine is 30 ships for 1M and right now the slots limit me to 150 ships max. If I felt "funny" one day and used multipliers those could be 300 big cannon ships in a 10M game. For the case of just 10 ships it is a really good idea though. Most of those ships end up in single ship blueprints, and various cluster sizes and it is some extra work to make changes to all the ships in all the blueprints. So your proposal makes that a lot more fun.
I don't think there is an easy way to limit the number of ships anyways. Even if the game simulated detonating all explosive charges and counted the individual pieces with control rooms people would still be able to game the system by adding dummy explosive charges close to their CRs that are never meant to be used except by the game engine when it attempts to count individual ships in the splitter. The most robust system is to just count CRs. I.e. You can have 10 CRs per slot, so either 10 small ships or 5 ships with 2 CRs, but never a 30 ship splitter like mine.
For Bounty Hunter it is a nice idea, but what if I spawn a splitter early in the campaign?