It seems like a plausible sequence of changes, though perhaps called into question by the fact that there doesn't seem to be an attested example (at least out of the sample of languages used on the aforementioned site) of a UA language with the vowel inventory /i ɨ u ə a/. indeed, it appears that /ə/ is only attested as a reflex of /ɨ/, and then only in Cupeño. Then again, the /e/ in Luiseño (which comes from /o/) was apparently in free variation with /ə/ for at least some speakers, and /e/ and /i/ apparently merge in unstressed syllables in that language. I have to wonder if the same might be true of Gabrieleño, another Takic language that apparently had o > e.Cedh wrote:(I don't know if that's the actual development in the relevant UA languages, but it seems quite plausible to me.)
Incidentally, Gabrieleño (a.k.a. Tongva) apparently has a pretty bizarre consonant inventory, if the uncited inventory on Wikipedia is to be believed. Which it probably isn't... >_>
Perhaps most notably, the page claims that it had contrasting series of bilabial and labiodental consonants, including /ɸ/ vs. /f/, /β/ vs. /v/, and /m/ vs. /ɱ/. I know that at least that first contrast is attested elsewhere, but it's been my impression that identifying [ɱ] as a phoneme in *any* language is pretty controversial.