Is there a roadmap for Krita 2020?
4.3 and 5 version

Krita 5 isn't planned at all. We also don't really do roadmaps, we sort of think of a theme for a fundraiser, and the year after, that's what we work on. Scripting, text, stability & performance, that sort of thing.

When is 4.3 scheduled ?

It's scheduled after we finish resource rewrite and 4.3.0-alpha is thoroughly tested by volunteers. Which will probably take some time. It won't be in December or January, I believe. (Especially now since the main person responsible for design and most of the code for the resource rewrite is unavailable, so we, as in people working on it, need to figure out what they were thinking based on past short discussions and meetings and the code itself )

When is Krita 5 scheduled for release?

That's a bit hard to say, and I'm really sorry about that. I'm still working on replacing the existing system for loading and managed resources like brushes, and that's something I've been working on for three years now, and it's still not done. And it'll need to be done for 5.0...