It's reasonably easy to pick up your repo and leave.

How easy is it to pick up your bugs and leave?

Private repos cost and there is, and will be, a sufficient demand for such a purpose. Between nuget for package mgmt and github (instead of TFS, etc) you are looking at having important, common pieces available. This makes it extremely comfortable to be in the MS dev camp and still feel that you can interface with others and be sharpening the sword in ways that enable you to build cross platform and potentially jump platforms as necessary.

People have seen experienced .net devs picking up in a wide assortment of communities. Some interpret this as mind flight, or it might just be that the .net ecosystem has made some wise choices that enable devs raised in the ecosystem to not feel their world has silo walls. It's less "no, this" and more "yes, and."