This is all pointless speculation, but I guess it's fun.
"Doctrinal" changes that would need reinforcement from the Elders would have to be significant.
Change in blood policy -- perhaps being totally a matter of conscience (really, not BS).
Adjustment in 607 for Jerusalem's destruction. This has to be the most common issue brought up to doubt it is The Truth. This would mean some adjustment in 1914 as well. I just can't imagine who at Bethel would have thought through all of the ramifications. Judging from the new literature, there are no deep thinkers on board any longer.
I would suspect more of a policy change to legally distance WTS from the individual congregations. This could include ending the CO visit arrangement, or at least his authoritative position. It could mean having the Cong vote or choose to associate with the WTS and all compliance would be more voluntary. This would require strict control on who is appointed as elders -- only loyal men. WTS could own KHs to gain some control.
Very reasonable possibility is change in "donation arrangement". Now that WTS is assuming ownership of all real estate (KHs), Congs could "pay rent" even after paying off KH, this would generate "donations" and it is similar to what already happens at Assm Hall. JW Districts build and pay for Assm Hall. WTS maintains ownership. Even after payoff, circuits "rent" Assm Hall for meetings at a rate that generously funds WTS. Arrangement could be just like per person "suggested" donation for CO cars & insurance, etc. If your Cong falls short, they sell your KH and move you in with some other Cong. (Hey, if this IS NOT the change, this is great idea for you guys at Bethel reading!!! I may have solved the cash crunch!)
Doc