As far as I heard from a Googler, they would like to completely overhaul the UI, but don't have the time. If they cannot achieve this, then the chance of porting SketchUp to another toolkit is rather low. Although Google massively applies Linux in its company (Maps developers, streetview etc.), they consider for their products mainly the market share outside the company (whereas the Mac OS X share is mostly a US phenomenon).
In the SketchUp Help Forum, there are rapidly increasing requests for a version for iPad, iPhone, but also Android and ChromeOS (?) users demand their rights. I think if Google will ever support another platform, then it would be the web.