Personally, I think it's a great idea, and here is the reasoning behind my thoughts:
1. Whittaker worked on Broadchurch with incoming show runner Chris Chibnall. He is obviously aware of her talent and wouldn't have cast her if he didn't think she could bring something fresh to the character.
2. She actually is bringing something fresh to the character, just by being female. I'm interested to see how a female doctor traveling with male companions plays out, in addition to the change in the way aliens/monsters react to the Doctor's presence.
3. Two other Time-Lord characters underwent regeneration related gender changes under Steven Moffet's tenure, the first of which was obviously the Master. The other was the General who first appeared in 2013s "Day of The Doctor", and again in 2015s "Hell Bent" in which the General's regeneration took place. At the time those episodes aired, I was convinced it was foreshadowing for what was to come (Guess What!)
4. Ginger Hair! Okay, so the 13th Doctor is blonde in the photos we've seen so far, however that could change. How? The answer is simple. The Doctor wishing to be Ginger has been a recurring gag since 2005s "The Christmas Invasion", in which David Tennant's newly regenerated 10th makes a random quip. Maybe the 12th Doctor will finally just give in and dye her hair ginger. We'll just have to wait and see.
Those are my 4 reasons! I'm looking forward to what "Doctor Who: Season 37" will bring our way! But until it airs...try not to get sucked into the time vortex.
