I have opinions twofold:
1. I have no issue with Time Lords being capable of this. I don't see why a species that frequently regenerates their physical couldn't change sex with each regeneration. I'd even argue that a female Doctor would be a good idea... if it were still the 60's. It just feels too late. With the Master it's different, they're an unhinged character prone to rash acts and suffering deep mental instability, it would be understandable to not have a solid sense of self. Alternatively if you're going to be so flippant with genders, it'd be something you did every couple of regenerations or so like the Corsair. But that isn't the Doctor. The Doctor knows who he is, where he's been and where he's going.
2. There are already well established female Time Lords: Romana, The Rani or Susan. When, in the history of television and film, has a gender swap ever resulted in a superior product? Who does it serve to take an established character and simply change their gender? I might just be approaching that sweet spot of mid-20's, white male crankiness; but it just feels lazy. It's almost like they're saying that they don't have enough faith in female leads or their ability to actually write one, so they're just going to take a male character that everyone already likes and use that as a springboard.
Megalodon said:
Serious question to any old-Who buffs. Is this whole 'timelords can regenerate as either gender, regardless of previous incarnation' something with an established canon pedigree, or something that has arisen purely in the tragically awful Moffat era (because I don't seem to recall it ever appearing in the RTD era)?
To my knowledge, the sex-swapping in regenerations is a NuWho contrivance. If I recall, the first mention we get of such a thing being possible is with The Corsair in The Doctor's Wife which was a Neil Gaiman, Moffat Era episode in 2011. Since then the fanbase has been picking at the thread and now we have this. Though they've been laying the groundwork pretty hard in the last two seasons.