So, as the IPv6 addresses are unlikely to be allocated dynamically (and thus changed frequently), this may work as desired.
One single not-really-a-problem raises only when the nodelist line contains INA:f.q.d.n flag, as the old mailers may be unable to detect EAI_ADDRFAMILY returned by getaddrinfo() or NO_ADDRESS returned by archaic gethostbyname()
Once faced, that may be solved by either: 1. Updating the mailer. 2. Checking that manually.
So leaving it up to sysops seems to be the best solution. And, of course, we should recommend checking for EAI_ADDRFAMILY to the developers. At least here:
* Originally in FTSC_PUBLIC * Crossposted in IPV6
-- Alexey V. Vissarionov aka Gremlin from Kremlin gremlin.ru!gremlin; +vii-cmiii-ccxxix-lxxix-xlii