Anything that involves new character models, like a "highlander" version of other races is very likely never going to happen again. It's been said before that adding races is an exponential challenge because that exacerbates the amount of animation work needed for nearly everything in the game, and animation is the most expensive and time-consuming aspect of video game design. It's not impossible that they can change their mind later down the line, but I would not place any bets on getting anything else in that regard.

That said, having alternative clans that do not change animations or have an effect on clothing are certainly more plausible, like half-Elezen Hyurs like Hilda, and I think having more mixed race options like that in which the base model does not change could be a cool thing to see, though there are still some limits as to what races you could have mixed characters from that wouldn't involve changing the base character model. I wouldn't hold my breath on anything like half-Lalafell, half-Hrothgar, half-Roe, or probably half-Viera. Miqo'te, you might be able to get away with something like Hyurs with Miqo'te facial markings or noses, but the tails and ears are probably a no-go.