actually the new ue connectors are the best i've seen, but i agree the old style ue, jh and westone ones are not the greatest (having just got my jh13 back from having them replaced), but are also fine if the socket is recessed. regardless of what your opinion is on balanced iems (i dont know about you, but having the common mode delete other peoples and my own cell phone chirps in my balanced jh13 fills me with glee and the bass response is better in my diy setup) but people do use balanced iems and this connector format is not ideal, it inferior in that regard to the standard connector. I make/mold my own connectors and use solid hard annealed pins, so the only remaining problem is the socket.
also, noise floor is a bigger problem on iems than any other headphone due to the seal and lowz high efficiency. higher current drive and lowz output are far more important for linear response from iems than comparatively easy to drive higher impedance loads.