#2 Gang wars
Zelina Vega hired Austin Theory as a part of her stable because it was in line with her gimmick of spotting the best talent and pushing them in the right manner when called upon to do so. And now, she can pretty much call upon anyone in NXT who's caught her eye. Why Austin Theory leaving the stable is important is because it can lead to some serious gang wars.
How Austin Theory leaving Zelina Vega's stable can initiate wars between factions
Very simply put, with Austin Theory in Seth Rollins' faction, you now have the Messiah, Rollins, the disciple Murphy, as well as Austin Theory making the stable a very strong collective indeed. As for Zelina Vega, she can call upon someone from NXT or even include Humberto Carillo in her collective because he lost to Murphy, earlier in the show. And both of these 'gangs' can go to war against MVP's stable in due course of time.
Remember The Attitude Era, with The Corporation, The Ministry of Darkness, DX, and The Nation of Domination? Could we see a repeat?