I don't think there is room honestly. Business outside of food and cars is mostly a binary world. Coke and Pepsi, Target and Walmart. If you want to be a 3rd brand, you have to be pretty unique or, just be the cheapo brand.
Xbox proved that there was really no point for them to exist. Xbox and PlayStation games are pretty much the same with just a different branding. Gaming doesn't really change if Xbox goes away. Sega doesn't have the money of Microsoft to make a high end machine and would effectively be competing with Nintendo rather than Sony. Could Sega make a Switch competitor and put Sega games on it exclusively? Yes. Would it work....
...wait a minute. Yes. I'd buy it. I'm all in now.
Realistically though, it would probably do a quarter of what the Switch 2 would do and that's probably not enough to keep them in business or make it worth it.