My sensei's dojo is set up like this. It does make for less painful high-ukemi since uke's force absorbs into foam blocks instead of the concrete.
I always imagined (if I ever have my own dojo . . .) that I would glue tennis balls to plywood for the spring base instead of using foam blocks or tires. I think this would allow decent shock-absorbtion without having the mat space at such a high altitude. If the base needed to be firmer, simply glue on more tennis balls. If the tennis balls dry-rot or wear out, they're not that expensive to replace.
Anyone ever try this? If so, let me know since I thought this was my idea.
If this idea is truly new, I want credit if you use it! Please write on the platform, "These are Dan's fuzzy balls!"