Uh... yeah that'd be nice, but that's not going to happen. Smash fans are not that rational. WFT and the Chorus Men both share aspects that cause Smash fans to rage and whine, such as no one expecting them and few wanting them immediately upon learning of them - as it's "another spot taken away from a more deserving character" to use common ideology - however the WFT was revealed right at the beginning - and therefore subjected less to being called a spot stealer (as there was still an open-ended roster full of possibilities at that time). On the other hand, Chorus men will likely be the last or next-to-last newcomer to be revealed, and even if it's unfair, it will act not only as a character unexpected and relatively undemanded, which people are usually iffy on anyway (to say the least), but it will be a nail-in-the-coffin to many for not only a specific newcomer they wanted, but any newcomers past that. They'll say "we ended the roster with this? This undeserving waste of a spot?". And the rage will pile on not just due to what the character is, but what the character isn't.
Which sure, isn't rational, but like I said, Smash fans aren't rational. Well, many aren't. Chorus Men won't deserve the hate, they'll probably be a unique and interesting character, but so was ROB. If ROB had not been revealed at the end but much earlier he wouldn't have been the scapegoat, and neither would the Chorus Men. WFT could just as easily have taken this position too if she was to be revealed right at the end. Timing actually does matter a lot. The only thing that will thankfully temper the reaction a bit is that now we're expecting the Chorus Men due to the leak, so it won't catch as many off-guard. However many still aren't familiar with the leak, they don't follow as closely, so there will still be some sort of backlash greater than the usual when it happens.
And yeah people will warm up to Chorus Men eventually as they do pretty much all characters, but it won't happen immediately. It didn't happen immediately with WFT either.
And as for Rosalina and Greninja, yeah they were unexpected, but you throw the masses a Mario or Pokemon character and they're bound to clap their hands. Those are the two series they request the most characters from anyway.