The enc(4) man page states ``all rules on the enc interface should explicitly set `keep state (if-bound)'.'' Defaulting stateful rules to if-bound on the enc0 interface seems like a good candidate for OpenBSD's reasonable defaults policy.
Looking at pfctl/parse.y, the main issue in implementing this seems to be that expand_rule() cannot tell whether ``floating'' was set explicitly or not, so it cannot override the default on a per-interface basis. (The obvious hackish solution is to add another bit for PFRULE_FLOATING, but that's gross.)
