That's another problem with the term. What part of any show isn't for the fans benefit? Even if we are to believe my interpretation of how KLK is deconstructing fanservice with those scenes, they are still ultimately about educating the viewer into a more thoughtful mindset on the subject. The wire is meant to give the viewer a look into what its like living in the ghettos of baltimore, what it's politics are like, its police force... It's hard to think of a story of any kind that we can definitively say has no regard for its audience whatsoever. Taken broadly enough, it can make the term meaningless, which is why I dislike using it for the most part.
My opinion is that Trigger is purposefully trying to divide the audience and stir debate (as is happening in this thread). Shameless fan service? Clever deconstruction? Trigger is giving ammo to both camps!
On the one hand, Ryuko and Satsuki's outfits (and some of the "embarrasing" situations they're put in, such as Ryuko being whipped by BDSM Gamagori) would certainly not look out of place in your average sexist hentai flick were female characters are purely fap material.
On the other hand, Ryuko and Satsuki are true main characters, they have strong personalities and carry the plot on their shoulders as well as male characters do in other shows; the fact that they are female is secondary. Moreover, there's quite a lot of male nudity in this show, which offers an easy rebutal to potential accusations of sexism. Last but not least: the plot actually justifies the nudity (to some extent)!
You see what I mean? Ammo for both camps! A similar reasoning could be applied to the treatment of incest.
It's fan service... and it's not!
This show is the anime equivalent of this:
GAFer, chose your side! #TeamBugs or #TeamDaffy?
Trigger is trying to have its cake and eat it too (as
Femmeworth wrote earlier)... and I think they're managing to do that pretty well! And as they do that, people are debating fiercely on the Web. No such thing as bad publicity!
As for your question, if mako just gets that for little narrative reason and it's really just to tickle the fan's fancy...it'd be wierd for Nudist Beach to have something like that, but they can easily throw something outthere to make it narratively justified. Whether it's fanservice depends on how much they justify it and how strict your definition of fanservice is.
It would totally be fan service by my standards. I still want it to happen though. After all, fan service is not inherently bad (and as you wrote, taken broadly enough, the term becomes meaningless).