had been using images for IPA. I think I should probably be able to use unicode these days and assume nearly everyone will be able to read display it, right?

No, as it turns out. The ipa unicode support is not acceptable in firefox.
ɑ
that's supposed to be a script a! script a! what part of script don't you understand? the turned script a works fine, though: ɒ

the triangular colon length glyph has got spacing issues, too. I can just use a colon for that, though I think. I'm not using ipa in page names or anything, i use own transliteration and transcription schemes for page names, which would use a macron, acute, or double letter for length before ever going into colon-type notations.

Tiebarred characters are only acceptable in default serif:
a͡i a͡ɪ ə͡i ɑ͡i
(though the "script" a there messes it up, because the glyph is messed up to begin with)
not default sans-serif (which mediawiki calls, and I'm happy for it do so):
a͡i a͡ɪ ə͡i ɑ͡i

growl.

Also, wikipedia lists SVG as its preferred format for "drawings and line art illustration", and I'm thinking it would be a really good format to do my writing systems in (though converting over would take a lot of work). However my install of mediawiki does not support .svg files. Also, I'm unclear on how well supported SVG is.

I should get all my scripts into .svg anyway, or at least some vector based format, and export to .png for now. I have many years of bad habits regarding file formats.