I think that viera men would be most successful and appeal to the majority of people requesting them if they were designed to be tall and conventionally attractive with a decent amount of muscle mass. A muscle slider could be available to put them anywhere between lightly toned to bulky. As for height, a slider could be available to have them be anywhere from just above a Midlander male to around the same height as a male Highlander or Au Ra. I'd settle for them having a similar height range to their female counterparts, if not a little broader.
I can picture them as being very classically handsome, with at least one facial option along these lines:
Another facial option could be more ruggedly handsome, such as along these lines:
A more androgynous base face option could be added for those who enjoy such aesthetics, though I think it would be very strange for viera men to be designed to be that way across the board given their established lifestyles. Thankfully the game has an established track record of favouring conventionally attractive character designs, so with any luck that trend will continue moving forward.
All of this, of course, is dependent on the missing genders being added in the first place which is not a guarantee.