Ok so now that I've had time to plan out how to word this as clearly and correctly as possible...
First of all, there's the legal implications of having a food service establishment. If you're going to create your own, there are many different licenses you need. You need a food service license as well as a ServSafe license just to start (source: I work in food service and have gone to college for hospitality). Not only that, the BCC probably wouldn't take too kindly to having a non BCC contracted food vendor in the convention space.
My next, and shortest point: BronyCon is a pony convention, not an anime convention. Maid cafes started in japan and are often found at anime conventions. I understand that BronyCon is trying to incorporate multiple fandoms, but this is pushing it.
Next, there are...... "other" implications. Even though its not the intended purpose, many people view maid cafes as a sexual thing. Argue this particular point all you'd like, but it doesn't change the fact that there WILL be attendees who have that belief and will likely go to the cafe with the wrong idea. If those particular attendees see a moderately attractive female dressed as their favorite pony and in a maid outfit, there will almost certainly be comments made and maybe more than that. Do you really want to make those female volunteers uncomfortable like that? There would have to be a HUGE security presence at the cafe to prevent anything like this from happening and that would stretch security moderately thin. Also, what do you think would happen if Hasbro got word that even though they were only cosplayers and it wasn't the intended purpose, the characters that are property of Hasbro are being sexualized. I don't think any of us want BronyCon to get a C&D.
In conclusion, while a good concept for OTHER conventions, a maid cafe is not a great concept for a convention like BronyCon