https://snowstorm.net/ is a different thing, it’s not Snowflake, but related.
I call it “Snowflake network”.
Precisely what you’re asking (Snowflake as middle relays) is not feasible because Snowflake code doesn’t use the Tor code. But the idea of utilizing NAT hole-punching for middle relays came to me as well , and I found this paper about this (namely section 2):
Tor and NAT devices: increasing bridge & relay reachability. Basically the idea is (at least the way I see it): NAT traversal requires third parties, which is not good for anonymity of relay users.
But perhaps a more decentralized way of NAT traversal could be found. 
Also see related discussion: Relays and bridges behind IPv4 CGNAT - #2 by WofWca