If any amateur radio folks want to use a v6 block that's been allocated to them for amateur radio/digital comms/etc purposes, there are probably plenty of folks who already have routers/bgp sessions/ASNs who'd be happy to announce their space for them at no cost. If someone doing so were to ask me nicely, I really can't think of a reason not to. It doesn't really cost me anything and no one's pushing enough traffic on ham bands to amount to enough to even think about the bandwidth usage under most circumstances. There's plenty of overlap between hams and people who want to support the hobby, and network operators with resources to spare. And if things don't work out, since it's your own space, you can take it and go elsewhere if needed - it can't be sold out from under you. 

Additionally, one can run their own bgp with extremely inexpensive gear these days. Ubiquiti's edgerouters will do it (around $100 USD), or a whitebox running pfsense or any number of other FOSS operating systems. You don't need multiple full tables from several providers plus a half-dozen IX sessions to announce a /48 for ham radio use. That same low-cost gear can tunnel the space to wherever you need it, too, if needed. Remember, we're almost always talking about very very low bandwidth applications here on amateur spectrum.