STOP THE DRAMA
I'm as surprised as you are, but keep in mind that Maria is not one to suddenly take these kind of important decisions without thinking about it.
This comes out of the blue to all of us, but I think it was planned for long time, as you can guess by the fact she said herself:"I'm excited to announce who the next coach will be!", so it's already decided and maybe they've already began working together.
I liked Thomas in the past three years, basically since I've been "back" watching tennis and even more than I ever did, I think (as I heard on TV comments sometimes) he improved a lot her claycourt game and I'm sure he's been a key factor in winning RG. I don't think it's anything to be afraid of, I guess it may be a good time (as she doesn't have much at stake right now) to move on and find a way to step up her game on fast courts and take it to another level.
I can't wait to see who she will be working with.