Now this is pure speculation, figured I'd say my piece since I just got back from work and saw the Switch.
I think this may mean two things for the Future of smash.
Scenario A: Smash 4 gets a port/update, and we have our absolute final game in a "Special Edition" with all the DLC and maybe 1 or 2 additional characters, with a true final patch. The port would support both the Wii U & 3DS stages etc, due to the dual nature of the Switch.
Scenario B: Super Switch Brothers in a few years time. With Sakurai at the helm or not, although how they'd top 4's roster is beyond me, Also with a name like that maybe a central mechanic could be switching characters every stock.
Regardless, with 4's success in both the competitive community and doing well on a poor selling console, I don't see them dropping Smash in the future, Melee & 4 are still both still pretty big events etc, and with Ninty actually sponsoring events and being cool with Melee/4 being on a stage. I could potentially see something perhaps more along those lines in the future, but call me an optimist.
What do you all think?