Wpf vNext is in the works although not many details has been shared yet except there will be some performance fixes.
There's been a lot of rumbling first that WPF was going to be discontinued and recently that Silverlight was being discontinued (!) in favor of HTML5. I'd wager a bet and say both these rumours are highly unfounded.
There's no way Microsoft will ditch the investment they've made in WPF and Silverlight to develop a new framework and it's certainly not probable that that replacement will be HTML5.
Microsoft's support for WPF has been a bit lackluster though, mainly because I think they're fighting tooth and nail to gain ground with Windows Phone and therefore Silverlight has been prioritized. I see three scenarios as likely (or a combination thereof)
Microsoft support for WPF will
continue to be a tad weak for the
coming years, not to say it will be
totally neglected or it isn't a
viable platform right now. It all
depends o what kind of solution
WPF and Silverlight get merged
into a more coherent whole.
Silverlight is pretty much a subset
of WPF anyways so it make sense and
would only require some
re-architecturing to allow for OS
level API's etc. This is probably a
good scenario since WPF then will get
the benefit of the Silverlight team
(which seems to be more staffed then
the WPF one)
Microsoft re-focuses it's efforts
on WPF and forges strongly ahead with
significant performance enhancements
and new features. This scenario is
slightly unplausible as long as
they're occupied with Windows Phone.
Anyways, if your application is a good fit then I'd say go ahead with WPF, worst case you have to do some adjustments to the WPF/Silverlight merge down the road (which is some ways of I'd guess). The only thing I would advice against was going with WPF is if it's a very graphic intensive application like for instance financial visualizations, ie animation and 3D heavy requiring a high framerate. Then WPF might not be the best pick right now.