"stable" corresponds to "iscachable" in PG < 7.3, and "iscachable" has been kept for backwards compatibility. I assume you've just listed those that weren't set "iscachable" ...
Since 5.0 is dropping support for 7.2 we might as well adopt the new terminology. Also we can just drop bittoint4 etc since these are implemented by casts in 7.3 (these bit functions were defined by PG itself in 7.2).
Should we do this for 5.0?