Seems to me like you have 2 choices with how you arrange your regulations. You can group everything by aircraft type, as per the old system that US Herk liked, where you have one huge manual that covers all rules, regulations, SOPs, tactics, etc etc. Or, you can group by type of regulations; so the tactics for all types are in the 3-3/3-1 series, and all the rules for operating aircraft are in a central document with chapters for all types, like the old 550/new MMA series documents, or GASOs.
There's merit in both and I don't think it's as one-sided as people here seem to be saying. Sure, the majority of posters here are operators, and therefore we'd like one big book that has everything in it, but things would absolutely still get missed if that was the case. A change to the way we regulate something that could just go in 550 (or whatever the new one's called) would have to be reliably inserted in every type's manual instead.
The current system seems to work. I'd quite like to see a simpler naming convention for some documents so I know what reference I'm meant to be looking for, but I didn't think there was much of a problem in moving from the ACM to the RTS to look up something for a particular fit.
Nowadays, most things seem to be stored electronically anyway, so looking at US documents wasn't too tricky. Rather than having to look at 10 different books, you just need 4 different PDFs open; which have the convenience of being searchable!