I agree with most things said, definite restrictions on length and width, but careful consideration needs to be made in relation to what dimensions these are.
Things like ease of paddling for maximum participation should be the core focus, unfortunately if sponsored athletes and the high performers dictate the sport it will die. A research into why and who SUP may shock the industry and make these changes occur. I know there is an increase in SUP surfers but the reason the sport has exploded IMO has nothing to do with the surfing side. It has more to do with the ability to walk on water, the view people can get into the water and surroundings but more importantly the fact that people of any shape or ability can do it any day of the week (including when the surf is out of control & the weather being crap) on FLAT WATER
I could rant on all day about this subject, but to open it up the sport needs to set minimum widths, length and design limitation, possible weight divisions and the majority of races for mass participation and viewer satisfaction on Flat water (this will also see SUP make it to the Olympics and mainstream)