Its a good question to ask, because at the moment, the boards are capable of handling down to 6 knots, but the kites are the limiting factor -
I think that's right...but no matter how efficient the kite a minimum wind velocity is needed. How much lower the viable wind speed will go? Probably not much lower. The race boards work well because they can efficiently help generate apparent wind (both upwind and off the wind) with efficient foils (skegs) and a good planing surface, but other limiting factors will enter the game.
A good comparison to look at would be the latest Americas Cup boats - amazing hull technolgy and aerodynamics at work, flying hulls upwind and downwind in 7-10 kts, boatspeeds hitting 25kts!! Pretty amazing stuff, but mechanically quite different. But the downside to this is that
1. They are afraid to sail the boats in over 15 kts of breeze
2. They cannot handle waves over 2m
3. The boats are super expensive
so it's always a tradeoff...hard to "have it all" in one boat/board
but great to see people still pushing it and getting better and better performance.
Don't get me wrong - I enjoy kiting in light wind, but at some point it is just a challenge to stay upwind and be powered enough to have a little fun w/ waves or freestyle.
As soon as you go downwind on a wave in 7kts wind you may lose all your apparent wind and have negative wind, and unless your board can constantly generate the minimum apparent wind it just becomes a struggle IMHO.