I have a strong preference against the "playersexual" setup because it compromises worldbuilding for a gain I don't find significant.
Main points against it:
(1) If companions are "playersexual" that comes across, over several playthroughs, as if either everyone (in the world) is bi or your companion group is pre-selected - in-world - for sexual orientation. Keeping every playthrough self-contained in my mind in order to avoid being thusly affected takes effort, and more effort the more I talk with others about the story, and it is a constant strain on my suspension of disbelief since the little voice keeps nagging in my head "things don't work that way".
(2) Sexual orientation is part of a character's identity. Having it variable makes them less tangible and relatable.
In general, I think it is important that some requirements of equal representation are fulfilled, meaning that there should a similar amount of female and male LI options and player characters of no gender and major sexual orientation should be limited to only one option. Beyond that, I find it perfectly acceptable that if you want to romance a *specific* character, you are required to play a specific gender. These are roleplaying games after all.
I've been affected that way in both ME2 and DAO where my favorite characters were not romanceable by player characters of my preferred gender. It wasn't optimal but I didn't have a problem with it. Should my favorite character only be romanceable by a character of the same gender there is some chance I would forego the romance since I find it hard as a rule to play same-sex romances (though Leliana's worked well, surprisingly), but I would actually prefer having to forego a romance here and there to having my suspension of disbelief strained by a setup I just can't believe. It could even enrich my playing experience since I could now imagine my player character pining for someone they can never have. In that case, for a more positive outcome I'd romance someone else. Or no one in the first place.
I also think that players' appreciation for characters in general should not be bound up in the romances so much. If I appreciate a character, being able to romance them is a nice bonus, nothing more, and neither story nor game design treat the romances as more than that so I find it odd that some players ascribe so much importance to them. I would like Miranda and Morrigan just as much if they weren't LIs, and probably talk about them with equal passion.
All in all, I find it perfectly legitimate that a role-playing game may require some adaptability from the player if they want to experience specific pieces of optional content, or specific outcomes. Perhaps not quite as much as ME3's ending, but some.