Marvel getting desperate
Changing SS to a woman is not part of that previous winning formula... I don't think they did anything like that during the Endgame era, other than The Ancient One (who is not particularly a "main character" in the comics. Important, yes... SS-level in a Galactus/FF movie? No).
I don't think it'd necessarily be that significant.
And I say that as someone who has a box full of Silver Surfer comics up in his loft.
It arguably depends on exactly what they're planning to do with the Silver Surfer in the movies. If it's essentially just herald to Galactus, Galactus wants to eat Earth, Surfer rebels, I don't think a gender switch has any real bearing on that.
If they wanted to get more into the Surfer's backstory, you could argue a gender switch does impact that, since it could be argued some of it is tied up with concepts of masculinity, and it would also alter the Surfer's relationships with other characters as portrayed in the comics. But even then, change is not necessarily bad. Potentially it could be more interesting, since, these days, some of that back story is pretty clichéd. They could of course mix that up without changing the gender, but ultimately, if they are changing the gender, I don't see that as necessarily a big issue. I think whether they do whatever they're doing well or not is far more significant.
And as far as the backstory, they also have a problem there, in that they already did some of the main parts of the backstory without him. A lot of that was tied up with Thanos and the Infinity Gauntlet. So I'm not sure where they'd be going with the Surfer anyway.