Not right away, at least.

The Nintendo DS isn't replacing the Game Boy Advance, says Nintendo.

Wouldn't that be paid mobile gaming?

The Switch will replace the 3DS, but there will probably be a short transition period between the two.

Sounds more like they don't want to cannibalize the 3ds holiday sales than anything else...

They should wait until Nintendo Switch gets released and see the sales of it before they make comments like that.

Too late to save 3DS Xmas HW sales but this could save SW ones thanks to supporting the existing user base with at least one more season of SW, and making sure they know it.

I think it should, eventually, if the new machine sells well.
I tell you why:
One single console is a more economical way to approach the market, specially when it comes to have a pipeline of games and marketing for these games.
WiiU, 3DS, and now NSwitch is just too much, no console will get enough attention.
I hope the thing sells fast and Nintendo can forget about WiiU and 3DS.
Of course, some games will still come out from third party, but Nintendo does not have to bother promoting them.
If you do have a 3DS, not to worry, there are 951 games released for the handheld. You can play those. If you play and finish one each day, you have something to play for the next 3 years.

If you have a WiiU, 712 games were released, play them.

Aren't they releasing Pokemon this holiday season?  That should help move some systems.

So what will replace the 3DS then? Or will it ever be replaced?I mean I wouldn't mind because I just bought a New 3DS XL last week and I'm loving it :P