One additional thing to note is that Blench is usually not the most trustworthy source for detailed phonological reconstruction. For starters, he mixes here different systems of reconstruction in the Austronesian and
Hlai proto-forms. In AN *e, *C, *S and *ə, *ʈ, *ʂ, in Hlai *b, *əy and *ɓ, *əəy are the same thing. If he weren't citing stuff from previous studies, I'd want to check correspondences first before trusting the data to not involve superficial look-alikes.
I've done a lookover regardless though, since most earlier Austro-Tai sources don't seem to be available online. I've also only used the sub-branch reconstructions of Tai, Kam-Sui and Hlai that Blench gives, not Ostapirat's proto-KD (for which I'd like to see what branch-level data it's really based on).
1. Final consonants are well preserved in both families.
– Trivial correspondences for *p *t *k *m *n *ŋ *w *y.
– Clear non-trivial correspondences are AN *ʀ ~ Hlai ɦ (Tai and Kam-Sui ∅) and AN *N, *l ~ KD #n.
– AN *q corresponds to both KD #k, and Hlai *ʔ (the latter with no Tai or Kam-Sui cognates, but maybe only accidentally). Hlai *ʔ also corresponds to AN ∅.
– AN *i, *u have both #close-type and #ə + glide -type correspondences in KD. Apparently in AN, earlier word-final *əy, *əw > *i, *u. (However, this could also be a post-AN areal change. I'm pretty sure I've seen *-i, *-u > *-əy, *-əw posited for some AN descendants.)
2. Basic vowel correspondences between final syllables are roughly AN *a *i *u *ə ~ KD #aa #ii #uu #ə.
– Makes me think AN may have gone through a Berber-style vowel collapse: short vowels > *ə, long vowels > short.
– One non-trivial correspondence is short *a rather than long *aa in Tai when AN has the root structure *CaCa ('eye', 'thigh').
– Correspondences for E-type and O-type vowels in KD are too few to establish much of anything. Feasibly they could be conditioned by penult vowels: e.g. AN *qudaŋ 'shrimp' ~ Tai *kuŋ (if from *kr-), Hlai *raaŋ; AN *bulak ~ Tai *ɓlook 'flower'; AN *duʂa ~ Tai *sooŋ, Hlai *hluuʔ '2'. Further fragmentation within KD is evident though, and actually even just the correspondences of Hlai *uu in Tai are pretty heterogeneous according to this data.
– Tai has also *ɯə ~ AN *a, Hlai *aa, always with a close penult in AN ('moon', 'vomit', 'taro'). Maybe we should reconstruct *ɯ…aa in Austro-Tai.
3. Medial/initial consonants are slightly more munged, but often still recoverable.
– *m *n are stable. AN *l, *r, *ʀ all ~ KD #r, except AN *bVl ~ KD #ɓl.
– *p, *t, *k seem to be roughly preserved (with some latter sound changes in Hlai). *ʈ merges into *t in Tai and Kam-Sui, but gives *tʃʰ in Hlai ('eye', 'louse'). '3' might have developed as AT *tələw > KD #trəw > #ʈəw > Hlai *tʃʰʷəw.
– AN *qVt ~ KD #ɗ in 'liver', 'black', presumably through *ʔt. AN *qətut ~ Tai *k.tɤt 'fart' seems to be instead built on the above-mentioned *q ~ *k correspondence. Compare also AN *qudip ~ Tai *T.dip 'alive'.
- AN *ʂ and *s both ~ KD #s.
– 'Snake' shows AN *ʂVl ~ Hlai *ly. Perhaps this was rather *sl (the actual reflexes are l ~ ɬ ~ s ~ ts).
– Similarly, '2' shows AN *dVʂ ~ Hlai *hl > most Hlai /ɬ/, some /ɗ/ or /tθ/. Perhaps rather KD #d(V)s > Hlai *tɬ.
– AN *b mostly ~ KD #ɓ, but #b in 'shoulder' (or is this just an intervocalic allophone?), #pʰ in 'mist ~ rain' (?!)
– AN *d corresponds in Hlai with both *ɾ ('alive') and *r ('shrimp'). The latter only gives /r/ in one Hlai language while other languages have velars, which could suggest reconstructing instead KD #d, #kəd > Hlai *r, *kr. However this "*kr" also comes from AT liquids > KD #r, so probably not.
– AN *z, *dž, *ď, *w only occur once in the data (the first three correspond to various voiced coronals in KD, the last to Tai *k ~ Hlai *ɣ) and don't allow for any conclusions yet.
4. Penult vowel qualities seem to be mostly lost in KD, but not entirely.
– Hlai penult *u (not preserved anywhere, reconstructed for cases of /Cʷ-/ in some but not all varieties) corresponds to AN penult *u ('plant', 'alive', 'head').
– Proto-Hlai also has a similarly reconstructed penult *i, but this doesn't come up as such in Blench's data.
– Penult *i seems to trigger *p > Kam-Sui *py-, Hlai *fy- in 'tooth'.