The best I can offer at this point is the prepopulated roster option.
It's important that every event that get's signed up for is done so manually, to ensure there's no "I just signed up for everything, I didn't know about this one" kind of drama.
The pre-populated option creates as much of a problem since it it "assumes" that everyone will be present for every raid and people just say "I didn't sign up for that the system signed me up". In my opinion, any drama that might potentially come from guild leadership deciding to use or not to use a feature of this site is something that individual guilds' leadership is there to deal with.
In my opinion, if you aren't able or choose not to provide something that is requested it shouldn't be based on what you personally may think will or will not cause guild drama, but based on what you are willing to provide for guilds to work with. This not meant as critism, since I greatly enjoy the service that you provide and think you do a great job, just an observation, about what standards I think you should use when considering a site owners request.
We also use a set raid schedule for 4 days a week and post it at least 1 month in advance. That means 16 or more separate sign up windows that people have to to open and use. I have members asking me if there isn't an easier way for them to sign up. Having a single list to check/uncheck specific raids by only opening 1 window or for those that never miss a raid to "sign up for all" or something like that would be a huge benefit to our guild as well.