Mono lead Miguel de Icaza likes Silverlight. He says:
It makes tons of sense for us to start looking at an implementation of Silverlight on Linux with Mono. There is already a XAML loader, it is the perfect excuse to use Antigrain for high-speed graphics and that only leaves the pesky media issue to be solved.
In fact, am kind of happy that Microsoft did not do the port themselves as implementing this sounds incredibly fun and interesting.
Microsoft should grab this offer, if it is serious about cross-platform. Although Linux currently only forms a small proportion of desktop operating systems, it is nevertheless significant; Ubuntu in particular is making a big impact. Mac/Windows only may be kind-of good enough for the USA, but that’s not the case worldwide.