Tl;Dr I'm pansexual so my thoughts may be a bit moot on orientation, but strongly lean lesbian so who knows, maybe useful.
For better or worse I've thought a lot about this as well as listened to my feelings.
There is little question that initial attraction is olfactory and there have been some pretty cool findings about biological / selection advantages conferred thereby. It's also known that women rely more on scent than men in the flirting / pairing dance and also that as transexual women, hrt enhances up our sense of smell significantly (as well as changes our own scents.
So it's not unreasonable to think that as we transition, we're going to begin to feel more open to men and certainly that's reported here, if not yet in any literature.
For me, I remain pretty selective about men I'm interested in, essentially I'm socially only in men who have a pretty strong feminine aspect. I've never paired off with a male in anything but casual / exploring / fwb contexts and I don't feel that changing.
That said, I've had my share of oral sex with guys (giving, never wanted receiving) and I have a pretty strong semen / body fluids fetish and I was open to the option of receptive penetration before surgery but mostly after so many good things had happened due to hrt that many if my negatives about males had eased due to feeling more positive about ME.
And now post op while I'm seeking out women by preference, I expect the odds of hookups are better with men and in some very real sense I just do want to get laid more often.
And a *big* barrier has been lifted, while I'm still open to anal play, vaginal has always been what I hankered for and so I'm far more interested in PIV (with women or with men) than I was in PIA pre-op.
So yes my bias point has been shifted but then I was fundamentally bisexual/pansexual already. And then again my consideration of exploring bisexuality originated after my realization I was trans.