As much as I like the idea, there may not be a lot of interest in the Flite Test community since most of 'em here are using that new-fangled "foam" stuff instead of good 'ol balsa. You're right about the big budget on giant scale planes, and that would keep most people from joining in on any contest. Electric giant scale motor and batteries are much more costly than the 3S 2200mAh that so many love to use. Heck, the engine I'm buying for my current L-19 giant-scale build is a used engine and still costs more than most people will ever invest in a single DTFB plane including electronics!
One day I'd love to see Flite Test come out with their own balsa kit, and rumors of that happening have swirled around for a while. If they DID release a balsa kit, a build contest would be a fantastic way to showcase it and get people interested. Model Airplane News did a "Build to Win" contest a year or so ago (
LINK), where all builders started with the same basic plane design (a low-wing version of a Stick), and they used this as the base to create their own design. (I ended up with an Honorable Mention for my effort turning it into a Navion).
Personally, I really like this type of contest. Everybody starts with the same set of plans, and then modifies it as needed to complete their vision. My vision was a Navion, but others made their planes into WWI era fighters, biplanes, etc. Anything goes, as long as you could still sort-of see the original design. Rules could be changed to let the builder scale plans up or down as they see fit. Starting with a generic "Stick" design gives you tons of flexibility in what the builder can do with it.
Just my thoughts on the subject. Time in the schedule permitting, I'd be on-board with a contest.