I think even if they do grow up together, Taemin will still be the uke. I mean, he has a soft heart with a need to care for someone, and that someone just turns out to be Min WooJin, who may actually be a devil in disguise. XD
Yeah, I could totally see the devilish side in Woo Jin even in that extra/special/side story.
Tbh I can't see Tae Min be a seme at all imo he doesn't seem like the person (with who he is now) to lead in a sexual relationship. I feel like Woojin would still be it :/
That in another world, where Taemin and that other guy grew up together and he never died, Taemin would actually be the seme in the relationship.