Well, no matter what, the main character is canonically bisexual. So he will still have those base physical reactions, just like a majority of bi guys would. The reason the straight, bi, and gay exclusive routes exist isn't to override any canon aspects of the characters, but just to give the player a way to avoid seeing content they'd rather not. The reason all of these characters are romance-able is because Lukas, the MC, has at least a base physical attraction to all of them, and they all feel the same way towards him. Put yourself in his shoes, and a "gay route" is really just a bi guy choosing to date men. You can imagine he chose to pursue men primarily because he may not have had much experience with that in the past, because of small-town heritage or whatever. So I think it's okay for him to still find the women attractive, even on a gay-only route ( but I do agree I'd like to see Sylas' sprite override Sally's on a gay-only route after the first interaction, instead of just censoring the female nudity ). I'm mainly hoping to see romance routes tbh. I don't really wanna just continue a harem or anything like that, because a lot of the stories that have been set up would lend themselves so much towards real romance and mystery, with finishing all the routes unlocking all the secrets of the game or something. Maybe, sometime down the line, after all the romance-able characters have been introduced, the player will have to make a choice on which romance they'd like to pursue out of all the ones they've "interacted with" so far? Because I can't imagine, if you pursue Professor Rojas, that he just wants a casual fling. He seems like the kind of guy who wants to love and be loved genuinely, not strung along and toyed with, same with Kit and Irvin.
I’ve definitely thought about introducing romance routes. Ideally, I’d love to include multiple options toward the end of the game, like individual romance routes and even a harem route. As you mentioned, some characters lean more toward romance than casual relationships, so it feels natural to incorporate that. That said, it's a lot of work, so it might take some time before it’s fully implemented! You're right about the MC being bisexual and attracted to both genders, regardless of the chosen route. I understand that may not appeal to everyone, so the best way to handle that would be to offer separate routes, one strictly straight, one gay, and one bi, so players can choose what suits them without feeling uncomfortable with certain content. However, the MC is still canonically bisexual.
All of that sounds great actually, and don't worry ab how long it takes. It's game development, narrative crafting, and worldbuilding all rolled into one, don't worry ab the fact that you need time to do those things. I'm looking forward to seeing how everything progresses. I wasn't expecting to actually be enthralled by the story, but there I am (oh and I have to add that so far, I absolutely adore all of the characters and the art style is so cute)