I agree, I'd rather see something else as well.
I was one of those people who never got to experience the original 20K. We always went in Oct. when I was a kid and it was always closed (although I have some great pics from the Skyway looking down at it drained). I was always completely fascinated by that ride, of course heightened since I never actually got to ride it.
I finally got to ride Nemo at Disneyland, and yes, it's very neat. Really being underwater (somewhat), being in a "real" sub, etc. - it's very neat. I rode quite a few times (during off hours when it wasn't a 45min+ wait). However, it's clear there are limitations to the system, and I'm sure it's still much more of a maintenance nightmare then they'd like to chew off again (especially in Orlando).
If we ever got another 20K ride, it would be wet-for-dry like Tokyo - they'd never build something like that truly underwater again. And it's doubtful they'd do a Nemo version since, as pointed out, we already have one in Epcot, plus we already have a faux-underwater adventure coming in TLM.
That said, I've love the Tokyo 20K to end up in AK - the squid is an animal, right?