I am a huge Doctor Who fan and well anything science fiction really and a lot of people reacted to the change negatively but I don't see any problem.

As @geekorner mentioned a lot of beloved characters in Marvel also experienced gender swaps and it was also perceived negatively but to me the change was good in the story arc. It even made Thor odinson more interesting as well in his unworthy arc.

Well going back to Doctor Who we had so many unforgettable versions of him like David Tennant who was an absolute delight as the Purple Man in Jessica Jones and I am waiting for his rendition of Crowley in Good Omens.
There is no reason I see that the Good doctor can't be a woman. Time will tell if it will be a good fit but to me I like it. Maybe we'll ll have in the future more diverse iterations of Doctor Who.

I wait as well and will support a show that I have watched for so long.