For the iPad Pro 11 nothing seems to have changed; my wife got me a Magic Keyboard yesterday and I secretly went to Apple Support to make sure that it’s going to be compatible with the 3rd gen iPP 11 (secretly because I didn’t want her to know that I might have to return it; she knows I’m getting the new iPad). They told me that the current MKB is compatible with the new iPad, and the Apple site seems to confirm that.
The only thing I’ve really heard rumored is that the 5th gen iPP 12.9” is a tiny bit thicker than the previous gen and that the current MKBs may not fit right with it. There has been speculation that the magnets may also not line up the same on the bigger iPad but I haven’t really seen that anywhere but here. But for you, the iPP 11 seems to be the same so older cases/keyboards should be fine.