I think there should be a rule change, but putting constraints on the light wind equipment will only hinder light wind development. I really think that one sail and one board should be without limits. since the wind limit is so low, otherwise i think the 6,3 rule is fine. This way heavy guys could pick a formula for lightwind slalom, or build a custom 120wide slalomboard and a 14m sail.
I have compared my isonic 127 against my f2 formula from 2006, and with my 85kg 190cm, I´m always better of with the formula if the wind is below 12knots.
I have a 9.5 sail as my biggest.
Compare these two videos
First is Isonic 127, second is formula, same 40cm weedfin and same sail.
The wind dropped of a little so i switched to the formula and it was easier to get going, although the formula is harder to pump. I think i was going faster on the formula in less wind.
Friend is on 17m kite
Maybe time to market a 120cm wide slalom board?