Honestly I pretty much guarantee the ending will be something along the lines of "Older Nanasawa decides to let go of Seto for the sake of her younger self, and is subsequently transported back to her own time where she is now in a relationship with Seto in the present.
Personally i think that would be a copout ending, having the Timeline sort All the closure out wouldnt be satisfying
I think she is gonna be sent back to her time in that playground and she is gonna seek out old seto and confess herself along with helping her revive her acting dream (and Call her a love virgin since that seto has litterally never experianced it)
Not the most inspired ending as it has been done many times in the past But i think it would suit this the best