I'm not surprised to see some frothing rage from so-called fans about this - frankly they could do literally anything and there'd be people up in arms about it. Honestly I'm not sure that that's any way to continue such an old franchise like this; people are blinded by nostalgia (the original films were great, but our memories blow them out of perspective) and if you keep everything the same, people are bored and find you uncreative, and if you try to do anything new at least some of them will hate it and feel that you've violated their beloved thing.
Still, if they do make Ren a Skywalker, I think that would be a mistake and a disappointment. It actually feels unlikely; it doesn't fit with the plot or tone of The Last Jedi, which was far more interesting than previous films and almost subverted their tropes a bit. It would be a shame if they threw that all away (The Force Awakens was good but derivative; I don't blame them for that - they still had fans of the old series frothing about it despite that it was literally A New Hope again with different actors - but I'd rather they continue in the direction that The Last Jedi went in).
I wouldn't be upset if The Emperor were back, either, and certainly not surprised. Kylo Ren is a much more interesting villain but he's still a bit lame and doesn't quite fill that ultimate bad guy role. After Snoke, there's kind of a gap there, and it's not like you can easily introduce someone new (and have us care about them) in the ninth part of a nine-film series. It kind of raises questions and so whether it works or not would depend on how you do it, but I'd be up for it.
Worst case scenario, #9 will probably at least be entertaining and better than the prequels (which, for all their criticism, were themselves mostly entertaining even though they weren't actually that good), but it's not like I'm not going to go and see it, anyway.