What is the best speaker for a smallish room?

yes, it's not a problem to put bass traps, although one of the two corners behind the speakers is not really a corner. The rear and right walls do not intersect at a 90 degree angle: each intersects at a 45 degree angle with a short wall segment (30 inches)

A very important aspect is that you are currently using electrostats, hence you will always desire an unboxed feel. I would suggest a pair of Manger Swings with a Zerobox subwoofer. The Swings do not play below 100Hz, hence a small room like yours will not affect it much. Below 100Hz just dial-in the amount of bass you require for your room, on the subwoofer. Simple, a very high end sound for small rooms.

Um, yeah, you could probably get as good a results as any stereo set up using the near active Sonus Extrema's, yes! (I say near, as they use a avery simple crossover).
The catch would be to attain as good of a set up as possible
with the speakers and seat, and to get a Rives PARC in the mix!!! (mandatory, at the very least). You will probably like the sound.
I do like the Extrema's myself. They have better dynamics than the Merlins.
good luck

The Manger Swings look like a very interesting speaker. I did not know it, thanks for the suggestion. They remind me of the Reference 3a Veena, which is a speaker I am considering, together with the Thiel 2.3.

More genereally, two or three people sent me private messages recommending Reference 3a for a small room, particularly the MM Di Capo. I have looked at the specs, and the absence of a crossover is an intriguing notion. I may give it a try, although both Thiels and this Manger Swings are tempting.

kataro micropures are amazing!
i could not believe the sound..also
usher stand mount speakers are worth a try too.