That will be a good plot for Spencer's route. Just think about all of the drama and I hope both the family will accept them IF this is added though.
Viewing post in Extracurricular Activities comments
It could always be made that if you make the right choices and both families accept Spencer's and the MC's relationship, one of them could "pop the question" to the other and end Spencer's route with them being engaged.
Since Spencer and the MC have know each other since childhood there would be little need for a long relationship before doing this since they know each other so well already.
I hope the story of them doesn't end in them just being engaged I would like to see more of them. Like they could have another continuation like prepairring for there wedding and a fast forward scene like at least a year later where the MC and Spencer's life is shown that would be a great ending but if they plan on ending the route early on it would still be great.