and,  if Nintendo starts to charge for online, will it make Wii U owners pay to continue  playing their online games? 

Nintendo has made it clear it is dong as little as possible for the wii u from here onn out-  They clearly have considered any new investment in it a bad one - otherwie thye owuld have done more and would be doing more for it so nothing would surprise me- 

I  am just curious how hard they will push/strong arm existing wii u owners to move on to the NX ASAP

Trust me... with Kimishima in power. Nintendo will be pushing Wii U owners to beg for the upgrade months before the NX launches. They are literally causing a drought for the Wii U owners. The console is basically abandoned since Star Fox's release. The only thing we'll be getting is washed up 3rd party games that were already in the pipeline. Which is almost none.

They'll give another year like they did with the WII ...

I don't know. Don't the servers on the 3DS and Wii U use the Nintendo Network instead of Gamespy servers for online gaming like last generation?

Didn't the servers on the Wii last a little while after the Wii U release? I'm thinking a year or 2 after the NX releases maybe?

My bet is that somehow the SCD will allow a united network for hosting, I think the whole idea of NX will be based around this in some way.

The Wii U servers are on now?

Probably 2-3 years, much like the Wii/DS online servers.

A couple of years hopefully

I'm praying that they don't pull the kill switch too early, especially with games like "Splatoon" and "Mario Maker" - those won't even be games after Nintendo pulls the plug.

The way that they're at it right now might be a bad sign, however.

The official word is that production of the Wii U will end in 2018. Here's hoping the servers are supported through the end of that year at least.