#1 Dolph Ziggler
Dolph Ziggler has been one of WWE's premier in-ring performers for quite some time, but his credibility is severely lacking, and a run in NXT sometime in 2019 would certainly rejuvenate his career.
Sure, we don't want to stack Takeover events with main roster stars, but reserving one match per Takeover for one would give the show more credibility and dream matches, so Ziggler is the next person we'd love to see there.
There's no shortage of dream matches for Dolph down there (Cole, Gargano, Riddle, Kushida, Dream etc), and given how stacked the current Smackdown Live roster is, this one is actually a possibility.
Unfortunately, it's probably not going to happen, but the thought of Ziggler down in NXT (which he would be perfect for if he was only just arriving in WWE) would get fans very excited, and add a new flavour to WWE's developmental brand.