Honestly, I really hope we have some variety.
Coming straight off of Innistrad the "no freaks allowed" plane, we are overdue for something besides humans.
That said, I do hope they don't just cough up the fantasy races and call it a day. Theros comes to mind.
I don't really care what they do with Kaladesh, but from an objective point of view, I agree this shouldn't be another humans-only plane. What do you mean by "fantasy races", though? Are you talking about the usual suspects in Magic like elves, goblins, merfolk etc. or about the anthropomorphic animals and folklore creatures people would expect in an Indian-themed setting? That said, I was generally fine with the races in Theros. Some of them had a few flaws IMO (gorgons, sirens, nymphs), but overall I liked what they did with them.
Also, when has
catfolk and
cat beasts being on the same plane ever stopped Wizards? I'd be down for some more tiger-folk to
panther and
leopard-folk.
Well, Naya and Bant were designed by different groups of people and started out as separate planes, so diversity is to be expected. Ravnica is another plane where that rule doesn't seem to apply, though, so who knows. But someone from Creative actually stated a few years ago that they try to avoid that sort of thing. Don't get me wrong, I don't think there's a convincing reason why tiger beasts and tiger people would clash, personally. I'm always down for more tiger folk, or cat people of any kind really.