I started building flatheads out in SoCal in the early 70's - and I can tell you there were very few guys building them. I didn't have a single friend that actually had a running engine - until I helped a buddy get his running (though he never drove the car). There were very few parts being made - almost all the performance parts were used, decades old and in many cases just worn out.
Today: There are more performance parts --> heads, manifolds, crankshafts, rods, cams, pistons, ignitions, carbs, etc - available today than 40 years ago (by a large margin). Other than a block (unless you're buying a NOS French one), just about every other part is available out of a catalog. What this tells me is that there is demand, or the manufacturers wouldn't be offering these products . . . it would be back like it was in the 70's.
I see quite a few "young guys" building traditional HotRods . . . God Bless them . . . as without them, we'd only have the restorers and and the 'show car' crowd - many of which don't want a plain old flathead (because there are too many other cars running flatheads!). I'm also enjoying the fact that the younger generations are actually building them much more for the fun of having/driving a vintage/traditional hotrod, than for building trophy cars that are only driven in and out of their trailers . . . it is back to what hotrods are supposed to be. I'll bet there are more flatheads on the road today, then probably at any point in the last 40 - 50 years.
I've helped a few guys build their flatheads - just to pass along some of the knowledge and I'm enjoying teaching others. The more I help others, the more I learn along the way. Also, this causes me to try new things, continue to experiment and see ways to apply newer technology to these old beasts (things like coatings, etc).
Keep building them guys - and put them in any type of car you want, just get em' back on the road!