They need to hold off bringing Bayley up to the main roster for a little while longer IMO, preferably the end of the year where they can then hopefully build Sasha/Bayley for Wrestlemania.
Sasha hasn't even had her proper one on one shot at Charlotte yet for the title. Have that happen at Summerslam, have Sasha win and then build her as a champion to see out the year. You then bring Bayley up right at the end of the year or even around the Rumble to a huge pop and huge excitement to continue one of the best rivalries this company has going into Wrestlemania.
I'm not convinced at all they won't screw Bayley/Sasha up somehow up on the main roster in all honesty but either way I feel they need to hold off a little and get everything in order before throwing her into the mix. Let Sasha establish herself, let Nia debut and find her footing, let everything get running smooth post draft before throwing potentially the biggest female star they have into the mix. Patience and simple booking and they'll have something special on their hands.
So with all that said, expect Bayley to debut tonight