I really don't like the silent protagonist thing very much. When I play a JRPG I don't try to place myself in the skin of the protagonist because the protagonist is someone else's character. In Suikoden V, the Prince has known his family and the knights for most of his life. His past is already written for him by the game's designers, and I didn't have any input. I didn't decide he loved his family, that's imposed on him by the designers. I didn't decide he looks up to Georg, that's imposed on him. Sure you get a choice some points, like with how to treat Lyon in the beginning, but in the end he still treats her as more than just a bodyguard. He's still obviously extremely distressed when she is injured and happy to see her when she returns. He still looks at her lovingly in the good ending. I don't play JRPGs to roleplay. That's what I play actual roleplaying games for.
Anyway, to attempt to segue back on topic... Regardless of sex, I think the next Suikoden's protagonist should not be silent and nameless. If the protagonist is built with pre-existing relationships with other characters, those characters should know the protagonist and their name. A silent nameless protagonist in a JRPG just hurts the story, and doesn't really add any worthwhile roleplaying.
Look at Suikoden Tierkreis for example. Sieg has a personality(even if it is basically the standard shonen archetype), and his friends know it. This allows all sorts of entertaining interplay between them. The only problem is that he doesn't have a set name, so every once in a while the characters have awkward lines like saying "Uh!" when the caption says "Sieg!" Obviously Suikoden Tierkreis' voice acting has allot of other issues, which aren't relevent to this discussion... and somehow I managed to get off topic again...
I really don't see any problem with having a female Tenkai except from a commercial standpoint. It's entirely possible that Konami will feel that their target audience would not appreciate a female Tenkai (or at least not a female Tenkai that would do the series justice). I think the thing that we need to look at the most to determine the viability of a female Tenkai is Suikoden 3. In all the other Suikoden's the Tenkai is a fairly typical main character. You spend the most time playing as him, and he's the clear military leader in whatever conflict has arisen. Three is unique in that the most obvious protagonists turned out not to be the Tenkai, even though Hugo is clearly the closest to your average JRPG protagonist. But Thomas is the Tenkai. He's the one who brings the stars of destiny together. The question is, just how well did this unconventional approach do? If Suikoden 3's unconventional style was extremely unpopular, then Konami will most likely not try anything particularly original or creative in the future, figuring that retreading the same old turf is for safer, and more profitable. If Suikoden 3 did really well, the chance of something unusual like a female Tenkai happening is much more likely as it shows Konami that their fans are not going to abandon them for trying something different. I don't really know how well Suikoden 3 did though.
No offense intended.
Dumb dumb Moira Brown
Dumbest chick in this whole dumb town
Dumber than old king kong
Uglier than a junk yard dog
I set off a nuke to kill you
But fate was just too damn cruel