Well, right now Nokia doesn't have any core OS software team. WP is done by MS and Symbian is done by Accenture. This leaves Nokia with Maemo/MeeGo and S40. Why they even bother with S40 is a mystery since there are several light weight OS'es available that will do the job just fine. But then again, S40 has always been a good OS, so maybe a change will not be worth it.

Samsung, as the second largest, does not have a OS on its own. Bada is the closest thing, but is based around a commercially available Nucleus core.

Nokia still got Maemo. If they manage to release devices based on that I will be happy. But I don't see it happening, I don't see the purpose, there is limited synergy with WP with such a venture. The obvious way would be to use a small team at MS to do this using WP.