Couple of things ...
Butler I am pretty sure graduates this year. There is a possibility that she chooses to move on with her life beyond basketball, or that she could choose to start graduate school anywhere in the country on scholarship with her last year of eligibility. Not speculating that she will, just that she will have that option should she choose to exercise it.
Geno, as is often stated on this board bases playing time and starting roles on practice and team needs and next year's team is not this year's team. No one next year 'owns' a starting role or any minutes of playing time, prior to the start of practice in fall 2017. Nor will they 'own' anything based on the starting lineup and minutes played in exhibition games or the first game of the season.
Next year's team would appear to have six players with the inside track on starting positions early in the season as listed above:
Crystal Dangerfield, Lou, Gabby, Napheesa, Kia, and Azura.
The fact that Uconn this year is playing hard to cover an obvious weakness in height suggest that Stevens might be preferred to either Gabby or Napheesa in a starting role.
The fact that Geno prizes guard play in his system suggests replacing Chong in the starting lineup next year with another guard is more likely than replacing her with a forward or center. Yes Lou can play some guard but it is not her best position, and yes Kia can function as a PG, but it is not her best position either. Replacing Chong with Stevens, means you are compromising the quality of play for two other starters, while weakening the quality of guard play on the team which in turn is likely to weaken everyone else's play.
Retaining the starting four with Dangerfield replacing Chong creates the same issue facing this years team - playing an undersized lineup against teams with much more size and depending on team speed and disguise to win the day. Geno has no real choice this year as the talent gap between his starting forwards and his bench is too great. Next year he will have more options with no apparent talent gap - Stevens should be that good.
It seems to me that a rotation of Stevens/Camara/Natalie/Napheesa/Gabby at defensive center, Napheesa/Gabby/Lou/Megan/Kyla at forward/wing, Kia/Lexi/AEH/Mikayla/Lou at 2guard/wing, and Crystal/Molly/Mikayla/Kia at PG is how the roster shakes out. If everyone is performing at peak in practice, the starting lineup will be Stevens, Collier, Samuelson, Nurse, Dangerfield. And that early in the season, those five and Williams will all be averaging 20+ minutes per game. Camara, Walker, Butler, Gordon, AEH, Coombs, Bent, and Irwin will be splitting the rest, with the first three likely to get 10+ minutes each.