Mir would be an interesting candidate as a former champion and also having a very consistent year last term. It really was low-key and he never looked like winning races but he somehow ended third. If Suzuki genuinely have taken an extra step with the engine he might be able to make a run. That being said, he needs his second career win sooner rather than later for that to be the case.
As much as I like Bagnaia, I suspect that Ducati's advantage has been negated and he'll largely be back on a level playing field with his main competitors. I'm not sure he's resilient enough for a title battle yet. He crashed out from the lead in three separate home Grands Prix in the past two years. That bothers me with him. For example, I can't think of once that Rossi crashed out of a race lead, can you? For Marc I only remember one occasion when the engine brake malfunctioned. Besides that, the greatest champions tend to keep it together when out front and the bike is working. Bagnaia not so much. At least not yet.