I've had loose foot mains on two boats now. Neither one started that way - I began by just leaving the slugs out of the boom except for the aft one.
The only disadvantage I've found is that in doing a quick harbor furl, you have to remember to tighten the outhaul otherwise the main just drops through the gap! I wouldn't worry too much about the mid boom sheeting in that with either sheeting, the prime vertical load is at the end of the boom. In other words - If you haven't broken the boom yet, going loose foot shouldn't change things.
I find it good to ease the friction at the clew to make it easier to adjust the outhaul. On boat #1, I changed to a longer low-friction car. On boat #2, main #1 I did the same. Main #2 (the current one with two full battens) I also went with a velcro strap around the boom instead of a slider in the track. No problems.
Hope this helps.