I think Serena's pretty as she is. Those hats are cute; why couldn't they make a comeback? I'd like to see her- and everyone else- rotate outfits a bit more, but whatever. It's not a big deal if they don't.
You're right that there's an awful lack of female challengers. But the only real way to do that would be to make Ash's main rival a girl, because showing dual gym battles every time? Ugh boring. Hopefully he'll have a female rival this time though. I mean why not, right? Since they're obviously balancing the gender ratio of the main group, then it seems logical that they'd get more gender equality into the series.
The solution people here generally use is to copy their previous post and incorporate it into their new message. Why you would refuse to do so is a mystery.
I will absolutely not turn it into a sticky. Those threads tend to die off fairly quickly and we have far too many stickies already. Bulba and Serebii have many more sections devoted to the anime than PC does and much more activity. What works for them often does not work here.