Whatever we decide the final wiki syntax is going to look like (and I'll write up my vision on that shortly), it's clear that to avoid massive culture shock we should transition gradually. With that in mind, I'd like to propose a change or two to make right away, and I'd like to get opinions on what the impact might be.
The first thing I'd like to do is eliminate the non-bracketed external URL syntax. Specifically, I'd like to keep the single- bracket syntax [url text] for external URLs, and double brackets for internal page links and images, and eliminate entirely the interpretation of URLs in plain text. It would simplify the syntax, eliminate the problem of punctuation after URLs, it would make all the image links report correctly (ones that look external don't show up as links on the image's page), and eliminate a whole bug-prone pass in the interpreter. I's also eliminate the auto- numbering thing and make a bracketed simple URL without text just show the URL like an unbracketed one does now. Finally, I would not interpret external links to images as inline images, so /only/ the [[image:]] syntax would work for images (though you could still link to external images; they just won't be rendered on the page).
I don't see that this will lose any functionality at all, but if I'm wrong, or this will break something useful, or if there's a lot of people who will scream, let me know.