I think it all well and good to go after a different demographic as the next Captain--an alien certainly comes to mind and why not a female while we're at it?
Having done that, you need a genuinely interesting and compelling character with a fine actor who'll give it their all in the part. Look at BSG
that had several extremely interesting women characters, some of whom at least in theory match a stereotype or two (at first glance). Likewise Doctor Who
and Babylon Five
as well as Fringe
and Game of Thrones
as well Dexter
. Plenty of fine actresses out there who could carry it off--many of them undiscovered!
One way to approach it (whatever the species or gender) might be to look at an archetype, much as Kirk was vaguely based on Horatio Hornblower while the character Honor Harrington is quite obviously Nelson. Some possibilities:
(LOTR) - a lonely, grim natural leader who only reluctantly leads at all.
Cyrano de Bergerac
- the utterly brilliant maverick, hiding his melancholy with busy wit, with a dramatic tendency to take all responsibility onto himself.
(Winds of War) - a professional officer with surprisingly lack of self awareness yet a formidable brain, iron will, strict sense of honor and who sees service as the highest value possible.