I think you could make a training rule that would function in the context of 'troupe play', yes. It is not any good for serial party play though, as it just becomes a bunch of hand-wavy book keeping. I mean, if you want training montages and a slower pace of adventure with long hiatus between them, just describe play that way, it doesn't really need mechanics! OTOH the version in the 1e DMG is just borked. I assume it was intended to suck up excessive quantities of cash that PCs were assumed to be accumulating in most games. If you took the 1-4 RP rating seriously and the average was 2.5, then you had to get almost 3x more gold than XP to advance due to training fees, which basically means you'd always be at level+1 -1XP blocked on training at all times and losing 2/3 of your potential XP. It just didn't work at all! Even if you assume all PCs earn an RP rating of 1.0 all the time, you are most often blocked by unavailability of a trainer, and at high level this becomes basically an impossible situation.