I think Nvidia working on the hardware with Nintendo really helps bringing them closer to a level playing field in terms of features and general support. If the Switch is supported with OpenGL and Vulcan, that should really help with ports from PC, no?
OpenGL and Vulkan likely will have zero effect on most developers. It's cool, and something that people making their own engines will care about... But it doesn't really make a difference to the average developer.
Ps3 used OpenGL but it didn't really aid to it being Easy to develop for.
In fact, all major platforms right now use AMD based chipsets, so there will be unique performance optimizations that likely won't carry over.
Remember all the nonsense about Nvidia cards and some games? How about cards that don't have 4k Ram? It doesn't look good.
The bottom line is, and it's really the only point I'm trying to make, is that most third party developers are going to build their game around the platform that makes the most sense.
You see more PC ports now because the architecture is so similar and the performance on PC is so much higher that sloppy, rather, less expensive optimization work is sufficient. It became more economical to release there than last Gen, where you needed to spend a lot of money (and more importantly) time on building a game that ran well on both ps3 and xb360. There was just no room left on the budget. Game development is expensive.
No matter what way you look at it, unless something big is missing from the picture, the is going to be some measurable amount of overhead in porting your game to switch. Heck, even supporting ps4 pro is a pain.
What will ultimately decide third party interest is what that overhead is. Is illogical to assume it's less than the other platforms. So will it be worth it? Time will tell, but unless the platform is crazy successful out of the gate, developers are not going to put strain on existing projects. They are already tight enough as it is. With ps4 / xb1 have over 70 million install base with an ever growing hardware future...
I just don't see it.