Really hard to see how this could be a positive in any way, absent other rule changes to keep the downsides in check. More roster spots just means more relievers/pitcher specialization, lengthening games and taking us further down the track of pitchers being anonymized like NFL running backs. Same thing with longer benches that promote more platoons. In both cases you'd see suppressed service time/arb salaries/FA contracts as a result, so aside from the extra service time days for the ~900th best player in the game, there's not much upside for players either. You could change some rules to hedge against this(double hook DH, overhaul service time), but you should do those anyway since there's no compelling benefit to upping rosters. The sport doesn't become more compelling with arbitrarily deeper benches, it's the opposite in practice in all likelihood.