I honestly think if you do away with FFN and drop the max limit then that would shut the pro-FFN crowd up and still suit the majority of Ao3-only participants. Have the cutoff be 700 works or whatever and be done with it!
I'm not sure if that would make people be quiet, especially because if you dropped the max limit to 700, that would be a large cut of 30%. It would mean that currently anyone whose fandoms are over 700 would immediately lose those fandoms. So even if that would get rid of the complaints (and I'm not sure it would) you'd probably get a whole bunch of unrelated people annoyed.
Re: FFN
I'm not sure if that would make people be quiet, especially because if you dropped the max limit to 700, that would be a large cut of 30%. It would mean that currently anyone whose fandoms are over 700 would immediately lose those fandoms. So even if that would get rid of the complaints (and I'm not sure it would) you'd probably get a whole bunch of unrelated people annoyed.