It's also probably a great way to annoy your RIR when they ask 'how the hell did you burn through your initial IPv6 delegation with only two hosts'
Since /56 seems to become the "easily available standard size" for allocations, using a /64 doesn't seem like to much of an issue, especially since larger orgs should easily get /48s? (But are /64 really accepted as routes? I would have imagined that to be also limited to /56 or /60 or so)