Inconsistency isn't a huge issue as there are plenty of game changers in the squad already, and Pjanic would add something different. Juve is the perfect environment anyway, players like that should be snatching at that type of opportunity.
Pjanic is a very good Plan B. It helps with AG negotiations, Pjanic is an actual good backup option, and it destabilizes the Roma camp when they're trying to hang on to at least one of Nainggolan and Pjanic and are trying to lower the total wages due to FFP issues while Pjanic's wants 5m with his contract running out in 2018.