Fairly incredible. As if it were possible for an NXT show to be any more unmissable, now they go and do this. I would venture a guess that some combination of the following things occurred:
1) They wanted to move a belt on a house show to boost future ticket sales. Presumably it's the kind of thing they can translate into more demand, higher prices, and maybe bigger buildings. Something like this will get everyone buzzing and looking for tickets.
2) Booking plans changed rapidly. From my understanding the next NXT tapings are on May 19, which was perhaps too late for them to wait for whatever it is they wanted to do next. It seems clear that whatever it is they intend to do, it involves Samoa Joe as champion heading into those tapings. The obvious thing is that it releases Finn's only real commitment to NXT which, with the heating up the Bullet Club is going through on the main roster, might mean big things. More interestingly it might mean big things happened very quickly, since they had a chance to do this at Takeover just a few weeks ago. The only exception to this portion is....
3) They intend to give it back to Finn. There have been a few occasions in house show history I can recall where a belt changed hands one night, only to go back a few nights later. This possibility probably shouldn't be ignored as there as still several live events planned.
Overall it's very exciting and it does give a lot of interesting ideas for the main roster now that Finn is free, but personally I'm hedging my bets just a little bit that they might be giving it back to Finn in the near future, before the 19th. But if they go into those tapings with Joe as champion, well, it's probably the dawn of a new era for NXT. Assuming Finn either leaves or loses a rematch, things are wide open for Joe. There's Aries (who dethroned him as ROH Champion many moons ago), there's the possibility of building up someone new very rapidly or going to a new signing (Bobby Roode could quickly make an impact) or the most obvious and most exciting course is to match up Joe and Nakamura. They would probably do amazingly well against each other in a stiff match and they're the two hottest acts in NXT right now. It's the perfect thing to sell a Takeover, maybe even one in Japan, as has been rumored.
All around very exciting and it seems the landscape of NXT has been turned on its head. Looking forward to more house show results and the next tapings.