Duo mid is more likely.
Some ADC's are a bit more independent now, so roaming support might be more popular. Since melee's take rift herald better, it's probably best to keep a solo laner top lane, and have the ADC (if they are mid) help out with either objective when it's time.
Basically, here's what I see happening:
Jungler and support keep vision control over both objectives. Should be easier if support is mid, so equal access to dragon and herald pit.
Tanky bruiser top lane either holds lane or pushes it, for the ADC and/or jungler to assist them in getting the herald. Support can help, to keep their HP from dropping too low. Rotating aggro helps.
Jungler and ADC manage dragon pit, ADC uses blue trinket to scout while support and jungler uses wards and clears wards. Bottom laner provides vision control of jungle entrances, to keep away nasty surprises. Bot laner either roams and takes out a priority target before taking dragon (don't want that Graves stealing it, after all), keeps bottom lane busy, or if they are a mage of some sorts uses their cc and vision control to hold off the enemy or at least stall them for long enough.
It's basically the same overall strategy, but with some variation. Speculation, though. People don't like change, and might stick to duo bot out of habit and flame anybody who tries any different (at least until pros start doing it, then those same people will claim they always did it and flame anybody who duo bots. Yes, this would likely happen. You know who you are. Shame on you.)