Illuminations is absolutely amazing. I doubt anything will ever be able to top that for me.
By contrast, Wishes is probably my least favorite fireworks show I've seen (that I can recall) at a Disney theme park. I still love it, but relative to the rest of the shows I've seen, it's my least favorite. That is my basis for wanting to see it replaced. If Disney can create (what I think are) so many superior fireworks shows, what's to say the replacement for Wishes! wouldn't be superior to it? Especially if it follows the Remember... formula, I think it's sure to be a hit.
I guess my retort to your comment, Steve, and everyone else here saying something along the lines of "I would be disappointed if Wishes were replaced" is: have you seen Remember...? I can't imagine people would be reluctant to hear of Wishes being replaced if they've seen Remember...
Here's how I would rank the MK-style shows:
1. Remember... (by a wide margin)
2. Holiday Wishes!
3. Summer Nightastic/Magic, Music, & Mayhem
4. HalloWishes!
5. Magical (DLR's Summer Nightastic show)
6. Wishes!