The sequels that currently exist to "Back to the Future" weren't exactly necessary. But, they were hugely enjoyable all the same.
Maybe this fourth movie could work. The thing is though, with all the time that has past, you really need an inspired reason to continue. And inspiration in Hollywood is not exactly in great abundance.
Hopefully, if they do bring it back, they bring back Zemeckis as well. "Back to the Future," after all, is probably the only great, perhaps even good, thing he ever did.
It could definitely work with some creativity, there really is no limit to things when you have a time machine involved in the story, anything could happen. But as you say inspiration in Hollywood is a rare species. But Zemeckis has no interest in it from what it seems and has said a 4 is never going to happen. At least not as long as he is around and can prevent it. I'm sure things won't stay that way after he has passed though. Hollywood is just playing the waiting game and surely is planning on milking this franchise dry.