This isn't a Kea replacement, at least not in terms of utility. Starfleet very explicitly does not care about the scientific capability of this ship, and would accept even just a basic science lab.
Which does make sense, seeing as how we've just designed the Attenboroughs. A sort of midpoint in engineering between a Miranda and an Archer would probably be our best bet in getting decent order size, but a smaller ship would probably help with that too.
The Attenborough fulfills a completely different niche compared to the Kea, which possesses:
[ ] 0: Small Arboretum (+2 Science)
[ ] 1: Secondary Computer Core (+2 Science, Advanced Computing)
[ ] 2: Dilithium Analysis (+1 Science, Dilithium Prospecting)
[ ] 3: Science Labs (+4 Science)
[ ] 4: Astrometrics (+2 Science)
[ ] 5: Biosciences (+1 Science, Biosciences)
[ ] 6: Geology Lab (+2 Science)
And I doubt the Miranda will have more than the basic scientific facilities mandated by the brief. With the Kea being somewhat obsolescent scientifically (thanks to the generalist labs, iirc, plus lacking the dilithium prospecting ability now) there are a few niches that are entirely unoccupied, and which will likely remain unoccupied for a while.
Of course, if you want to discount science modules it should be remembered that more advanced engineering/utility ones are typically 'fuck huge' and the command configuration saucer kneecaps it at basically 3 decks at best in the saucer.