Of course Nvidia and AMD will say "No!", for now.
They have a lot of software to write and support and Wayland which is not even deployed yet anywhere is the least of their worries.
In like 4 years Wayland will be running well and native on Ubuntu (on top of open source graphics drivers) and X will already considered pretty much an obsolete technology - that's when the folks from Nvidia and AMD will start thinking about supporting Wayland.
Hence the open source drivers are the (only) way to go for Wayland for now, which shouldn't be news nor surprising.
The open drivers will work well for current graphics cards because the drivers will have matured by then. New cards will be left playing catch up as always.
What does matured mean in this sense?
How long does it take for graphics drivers to reach that point, after the hardware is released? How long does it then take before this hardware then gets ignored, and the support deteriorates again? How large is this window?
Also, how is this point defined at all? Is it the point where this hardware is working as expected, or is this the point where your expectations have dropped enough?
(yes, i am an actual graphics driver developer, with way too much experience and with far too good a grasp of history)
At least Nvidia said it doesn't mind people creating open source drivers for their hardware (which is very good if you think about it), unlike for instance Microsoft, who recently vehemently opposed the intent of a third party to create open source drivers for their newly launched "Kinect".
As I understand it, Nvidia doesn't offer open-source drivers because they're afraid they might be infringing some patents which would show up in the source code.. (I heard many companies do this for same reason, don't we all love software-patents?) but then I don't know why they won't even release documentation since AMD doesn't have (serious) problems neither with the source code nor with releasing documentation about its hw.