The operative parts of the description were: "Can fanfic writing and QUILTBAG activism potentially intersect? What does it mean that fans of works with cis, straight characters are looking for more variety in the fiction they consume?" And the panel was pretty much about the second part and not on the first.
Three of the panelists identified as cis women, one as "it's complicated", and one as a trans man (the mod); four, I think, as bisexual or pansexual, and one in a way that I can't remember. No cis men, no gay men. So the mod started by asking about the balance between character dynamics and porn in m/m slash, given the vanishing rarity of men who are writing or reading fic; do they increase familiarity, or promote fetishization/objectification? (There was an unfortunate moment here when the mod was asking the audience to raise hands to self-identify and people perceived that they had been excluded—I lost track, honestly, of the categories so I can't say whether that was actually the case, but one person I spoke with afterward asserted it was so.) As I recall, the panel was generally "well, it depends?" to this, which also as I recall set a trend, but I was not taking detailed notes. I know I said I was super-uncomfortable answering the question about whether men felt objectified by slash, because, well, not one! (IIRC the mod did not answer this question in terms of his own opinion.) I seem to recall that we principally talked about characterization and emotional content in terms of how a story fell on the spectrum.
The mod then asked about genderswap fics, whether they promoted a fluidity in thinking about gender roles or reinforced a gender binary. Again, it depended; we talked about the difference between "literally had body changed" through tech or magic, which seems rare these days but was often problematic when it was more common (dysphoria as comedy, tragic trans characters), and Rule 63, AUs in which a character has always been a different gender (usually cis female) than in canon. It's true that these are rarely AUs in which the character is a trans person instead of a cis person, but we thought that was partly definitional, because there is definitely an uptick in "such-and-such character is trans just because we say so," and those aren't labeled as AUs but as head-canons (Carlos in Welcome to Night Vale and a couple of characters in Pacific Rim are pretty prominent examples). Anyway, Rule 63s, I have a weakness for them when they explore a particular character's challenges and character when confronted with a different set of gender norms, but it's an entirely valid perspective to say "why not use a minor character who is canonically a cis female and explore her," too. We talked about stereotypes and how those were likely warning signs (though may also be a result of very new female writers working through their own feelings about gender roles by using Rule 63'ed characters as self-inserts), and . . . some other things, which escape me now.
An audience member asked about works that put male characters, especially, into nominally-queer relationships and situations, but seemed to them to often just be replicating heterosexist gender roles, could those really be queer? I think it was here I mentioned a guest post at the Book Smugglers by Foz Meadows which was super-long and probably the first half could be skipped for people who were familiar with fanfic, but which had interesting thoughts about the subversiveness or lack thereof of certain types of fanfic.
There was also a question that I thought at the time the panel didn't handle well; on thinking about it more after talking with someone about it, my suspicion is that the moderator thought it was a question about why there weren't more stories without sex in them (which, AO3 search is telling me there are no Teen and Up rated fics right now, which is transparently false, but it returns 415,411 stories rated general audiences; 250,357 rated explicit; and 227,029 rated mature). But I'm fairly sure it was actually a question about representation of asexual characters, which of course is not at all the same thing. So that was not so good. (I know there were a bunch of asexual!Sherlock fics when Sherlock first hit, and as with trans* characters I've seen a few asexual-(or-aromantic)-because-I-said-so fics go by the tags I watch, but less than with trans* characters.)
There was a question about representing trans* characters as a cis author, which resulted in the usual "research; don't be afraid to write people 'not like you', because almost all characters are not like you; but if you don't feel it's appropriate to tell those stories, support trans* authors through cheering on/recs/etc." response. (I got to introduce the Magical Minority Fairy, or rather her non-existence, to another panel audience, yay.)
I don't remember much else; I don't know if "um, it depends" collapses down really small in summary or I'm just forgetting stuff after a long night. But I'd like to brainstorm updated fanfic panel descriptions for next year. Four years ago at WisCon we did Fanfic 401 (operative portion of description: "bisexual invisibility, the erasure and/or marginalization of female characters, authorial intent, trigger warnings, underage audiences, and source problems"), for which I have no notes but which was too overstuffed by far; at Readercon also four years ago we did Borders (if Any) Between Fan Fiction and "Original Fiction", which was way less 101 than I expected; and the year before that, Fanfic as Criticism (Only More Fun), which could probably be less 101 than it was. Do those prompt possible topics? What else: underrepresented identities? The fic we'd like to see (some of us don't write, you know, so we just have to wist in fandom's general direction)? Speculative fiction ways of looking at gender spotted in fanfic? Promote your very fic-able fandom that has canon underrepresented characters and a low barrier to entry?