As much as I would rather push my fellow Wii-U owners to get themselves a Switch ASAP..............I don't think I would ever suggest getting rid of their Wii-Us in the process.
Now trading in MK 8 on the Wii-U for the MK8 DX version on the Switch, yeah I can endorse that. And to an extent, maybe even trading in the old Wii-U Splat 1 for the current Switch Splat 2. But your entire Wii-U console itself............nah, not yet.
Virtual Console is still a damn question mark and with more silence and some "rumors" of another additional delay, I'd hold onto the Wii-U for VC alone.
Then of course the "Smash equation" has yet to be answered for the Switch........so you know holding on to the Wii-U for Smash is also a no-brainer as well. Same can be said for Mario Maker.
Look, I've given Wii-U a ton of **** since the Switch started booming in success (mostly due to Wii-U's poor release 1st party titles and lackluster marketing), but ****.......I wouldn't get rid of it. If you have a Wii-U, don't give that **** up. Hell, I haven't given up my old white Wii console from back in 2005.......and lord knows nobody plays on that thing anymore UNLESS you're in a retirement home forced to play Wii Sports for rehab OR you love to replay Super Mario Galaxy on a monthly basis (although most people replay Mario Galaxy 1 and 2 on the CEMU emulators now).
TL;DR: Don't give up your Wii-U console, even if you play your Nintendo Switch more.