Unicast IPv6 addresses are required to have a 64 bit interface identifier and a 64 bit network identifier (e.g. /64), handing out subnets lower than /64 is not spec compliant.
Network operators can do crazy things, but if you color outside the lines things may break.
AFAIK, it's not strictly true that unicast addresses are required to use a /64 network identifier.
It's common, almost necessary even, for environments with dynamic clients to use /64 subnets (precisely so that SLAAC works), but in a static environment it's perfectly fine to use prefixes larger than /64 (e.g. delegate a /80 to each individual host in a datacenter, for virtualization applications etc).
Hence, I'm wondering what the spec is you mention that is broken?
and to your point, yeah you can step outside the spec and things can work in controlled environments, but "there be dragons" when your dealing with interoperability on a large scale (in this case Android expecting /64s per the RFC)
Network operators can do crazy things, but if you color outside the lines things may break.