This was a great series!! I'll miss Saiki :')
As for him not telling his friends after all... C'mon, guys, he's already seen that they'll accept him we've seen their reactions why waste time showing what we've already seen. Asou was gonna end it even more open to begin with. You're free to imagine whatever you want after this. I absolutely relate to the desire to see stuff happen in canon though. But at the same time, this is a gag series, so all that matters is that it's fun and it was!
Also, Saiki x Teruhashi can't sail w/o powers cuz he cant fight off her fans without powers.