LOL, this is literally their server, they can do pretty much whatever they want.
Is it fair? Nope. We are like guests, who really matters - from the point of view of a business that is free for everyone - are those that donate.
I'm not saying either that they will only care for those that donate, like giving preference(like support and other stuff) to the donaters over the non-donaters.
They are probably doing such thing so they can use the x10 realm for another thing, or even use the x100 + x10 server to fix the x100 crashing issues(because they'll have 2 servers working on one realm).
I'm quite neutral - not because I don't play on these realms - to this, because there is still the possibility that they can do another realm, it could even be x4/x5. The news that they would merge x10 and x100 just surprised me due to its sudden reveal, they should have warned us before so people could set up their characters or something like that.
This crossrealm lacked preparation and testing, the crosstest realm that we had was literally useless.