This is a quite interesting thread
Here we have had the big door as the super lightwind board earlier.
Has almost dissapeared nowadays, except for beginners who like the "TT" principle
Raceboards are evolving huge, and if you just mount standard not too big fins, it gives a very easy ride.
Also, many riders have changed to directionals regarding waveboards, so it is more natural now.
And kitesurfers are getting better, meaning, the jibe (and tack) is a nice challenge to play around with (or easy to handle for many nowadays)
NOT as soft as a "round" board, no - but you get a very very fun ride, meaning you can handle chop easy, and best of all - you can now play around, going upwind and race downwind (no more riding back and fourth only), and you can JUMP HIGH in almost no wind
Kelp and/or extremely low water could be challenged by mounting smaller wavefins instead - as the board outline would still do the trick regarding early planing and speed, you would just go at a lower angle upwind.
Somehow the door seems a bit like a boring antique (sorry if I hurt anyone by saying this - I know I am also an antique with my age
), thus not that popular anymore like it used to.
But the door is VERY easy to ride of course
(except for some chop issues, but thats it)
Regarding the original question about surfboards, the answer is yes, you CAN make a big wide flat fish board, that would be able to match a Door in light wind planing.
But I am sure the fun factor is almost non-existent now
(at least for me, it degraded very fast - the fun that is...)
With a door you can make jump transitions for example, and other stuff.
With a raceboard you can jump high, and "get around".
With a big strapless fish you can do nothing of this, and you are stuck riding with very low speed and can only do slow jibes and tacks trying to keep the fun factor alive
So these boards got very boring very fast
The worst of it all, regarding a big fish, is that if the wind picks up even for short moments, you are just stuck with EXACTLY the same (low) speed, tug tug tug
With the door or the raceboard, it REALLY is a blast when you get a bit more wind, as you just accelerate and can now go really fast (really fun) and upwind and jump MUCH higher suddenly - YEAH
If you should have a more fun "almost" light wind tool, a strapped wide waveboard with a flat rocker, and not too long, would be the way to go
As the apparent wind you get strapped (especially in chop), when planing, is much more fun and way better for power than huge strapless surfboards IMO.
But Hey - a strapped wide waveboard with a flat rocker ? That is in fact a raceboard with small fins
Have been through all of the types myself (and many others like Malibu boards etc), in searh for the best light wind weapon, giving me the most fun.
Cant say for others what they prefer, would just share my experiences.
PS: Strapless is awesome in "normal" conditions with waves - I love it, but thats another issue... Just not good for ultimate light wind.