Western 3rd party support, i dont think they will by any, to be honest. Maybe some of those indie studios like the ex irrational games (bioshock) now called ghost story, those might support.
Japanese 3rd party tho, they are all gonna flock to the switch. No its not gonna affect PS4/XB1. Its gonna affect PS vita, currently it can still survive in japan, but with the switch coming out, it will eventually die in japan as well. And ofc 3ds. Nintendo claimed it won't affect 3ds. They said the same thing abt gameboy when ds came out. Gameboy died almost immediately.
seriously though...dedicated handheld gaming is only thriving in japan.....in most part of the world, dedicated handheld has all but shrinked, replaced by smartphones...whether we like it or not.
the 3ds survived the smartphones onslaught due to the strength of pokemon and other nintendo franchises......remember, it's the nintendo franchise that kept the 3ds afloat for the rest of the world (excluding), not the other way around. 3ds sales are way down when compared to the DS..
and before you said the video games market is shrinking, no it's not. The PS4 already look set to upstage the PS3 even at this period in terms of sales (not sure about the ps2 though but the ps2 is the best selling home console in human history so it itself is an outlier)...it is only the dedicated handheld market that is shrinking. Pending any major screw up by sony or upset by another company, the current trajectory is that the PS4 will outsell the PS3 and PS1 but not PS2 and become the 2nd best selling console in history.
Nintendo is wise to play to its strength with the switch but let's not kid ourselves here.......The Switch will not initiate another Wii like phenomenon....
getting japanese 3rd party is great but most of the 3rd party it will get are the 2nd tier 3rd party. Again, it's not going to run FF16 or Kingdom Hearts 3. More like another toned down version of the PS4 version of Disagea.
Just for reference, the top 3 best selling console of all time.
1) PS2
2) PS1
3) Wii
If including handheld
1) PS2
2) NDS
3) PS1