KV did look at this briefly, but then went and got a job. As far as IO know no one currently using Quest (including KV) has the background in .NET that Alex talks about in that post, so there is nothing happening on it at all at the moment. I would like to at some point, but it is years away I am afraid.
It may be possible to get Quest working on a Windows emulator on Linux.
If I remember correctly, Quest is built on an odd blend of WPF (Windows Presentation Foundation) and its predecessor WinForms. This is about the only part of the .NET framework which is not supported on WINE, and probably never will be. The advice on the Visual Studio forums seems to have been "If you are intending your project to be cross-platform at any point, just don't use WPF. Actually, just don't use WPF ever because it sucks."
Oddly enough, on the WINE forums the requests for WPF support only seem to come from people who want to use Quest on linux. The guys behind Mono have said they have no plans to add WPF support because it's unpopular, difficult to work with, and obsolete (in favour of Silverlight). It seriously looks like Quest is the only WPF app out there, so nobody's likely to put in the huge effort necessary to make it run under Linux just for us.
I have considered translating the Quest core to another language; which would be a very large project, but not unmanageable. But don't count on it happening any time soon, as the majority of my time has to be devoted to things I can actually get paid for.