I understand the question, but really - how big is the "demand" for such a thing ?
I mean, most riders are either strapless or strapped - so they dont want it.
..........Sometimes demand is created by designing someting new
...........If you build it they will come
.......Never say never
.......Never stop dreaming and imagining
As a matter of fact, with directional boards, I always want to switch between strapped and not strapped during the same session. Strapped for jumping. Unstrapped for upwind and jibing, a case when the back strap is inconveniently in the way of foot freedom.
Sound very odd to me
Of course some has different preferences than others - but I've never met anyone where the back strap is in the way for jibing nor upwind - as you never place your foot that aft going upwind nor jibing
If less experienced, I would without doubt say that the strap was placed very very wrong
When placed where used when riding waves, it never gets in the way for jibing nor upwind IMO, and as I've seen around
But footstrap placement is extremely important - and I've seen very very experienced wave kiters who dont really know how to find the "ultimate" position (as there ARE a single ultimate position on most boards for a specific rider)
Having found the best setup front and rear strap, can turn a "dog" into a "perfect" board
My point here is, that I believe many havent found the best positions, nor bothered - so they dont really use the board well - and would prefer strapless then...
But if you get it right - you will love riding strapped
For most "typical" waveboards, the rear strap is placed between the front fins and the rear fin when thrusters.
A few might like the strap almost over the front fins, or very close - but definitely never forward of the front fins
Just the most used and preferred position by most riders IMO
True, there can be board differences, yes - but still a quite good thumb rule, just behind the front fins with the rear strap (used for jumping and waveriding in steep/good waves only of course).