Any conference with more than 12 members for football is too large.
On top of that, there's a basic flaw in your premise: you assume the move toward superconferences is a collaborative approach. In truth, it's a dog-eat-dog scenario. So it's not out of the question that the B1G might go beyond 16, particularly if Delany's approach is to expand the footprint one state at a time, with the ultimate goal being to get to Florida.
If > 16 proves unwieldy for scheduling purposes (for my money, anything > 12 is unwieldy for scheduling purposes, but nobody ever listens to me), don't be surprised to see the B1G drop a program or two, nor would I say that it's automatically only the newbies that are on the potential chopping block. Among existing members, I could see Indiana, Purdue (although not both of them), Illinois and Sparty all potentially on the chopping block, and add Northwestern to that list (as well as the possibility of both Indiana and Purdue going) in the unlikely event we were ever to join the conference.