In terms of foiling in kitesurfing it has been around for quite a while but it is only now starting to gain some real momentum and make a break into the mainstream world of kiting, with a kite the foil presents real and established advantages ( extreme efficiency in low winds) yet it is still rare to see foils out on the water with foil riders only making up a very small percentage.
I think it will be quite some time before the advantages of foils with sups are established enough that people are going to want to invest the money and we see any real numbers out on foils. I can't imagine sup foilers tearing through the lineup will ever be a real issue.
One big disadvantage with sup foiling as opposed to kite foiling is with the power of the kite you could stay up on the foil at all times and navigate shallower waters ( if all goes to plan) with a sup you would only be up on the foil when your powered by the wave, as soon as the wave stops you would drop back down and need deep water to be able to paddle ( you would be doing some serious wading) surf foiling on a sup would only really be possible at deep water Bombies or shoaling barely breaking waves, I would say 90% of the surf breaks would be safe. If they could really make foiling work for downwinding or even a foil that can get up and stay up under paddle power we would really be onto something.
I personally am planning to get into kite foiling in the next year or so but this could be a dangerous time ( for a self employed person) because if sub 10 knot conditions become legit fun I may never get any work done again