Well, Visual Studio Code[1] is, so it may be coming in the future.

1: https://www.visualstudio.com/en-us/products/code-vs.aspx

They're entirely different products, Code is built from the ground up. So I'm not sure it makes a cross-platform Visual Studio more likely.

I would say the fact MS is shipping products on Linux, considering their historical stance, makes it more likely, but your sentiment is probably correct in that it may not mean it is likely. Ten years ago I would have laughed at the idea. Today, I have to think quite a bit more about whether it's likely.

I would not use the existence of an editor built on web technologies as opening the possibility that something as entrenched in Windows as Visual Studio would be leaping to cross platform.