I don't think this potential instance would be anything other than mutual and there's not really a need for Shinwoo and Seira to really delve into each other's minds. They're both young by their respective kind's standards and morally pure.
That sounds like "We were young and naive, we formed a contract, we didn't know"

Except Seira has a very deep sense of responsibility since she wants to be accepted as a clan leader and thus she always behaves as a clan leader should.
In my opinion a contract between Seira and Shinwoo could possibly happen only as a desperate move. Nobles are supposed to protect humans after all, not give them power to fight in their stand.
Frankenstein was just an extremely special case. The guy was already clan leader level and had kind of made a pact with the devil using the Dark Spear showing he was ready to use desperate measures to fight and kill. No turning back or peacefully play video games for him. Also, Rai formed the contract because Frankenstein in his berserk mode had so much power that the alternative was to kill him. So the contract was more to control him and rehabilitate him under Rai's command.
All that aside, I would definitely want to see Shinwoo getting a power up and become like Tao level or something like that. Maybe Krans level? Still ok. But the problem is that the power level of the opponents is now so high that even if that was to happen then he would still be a fodder.