Feature Request : iface may be allowed as datatype in all ipset

Is there a reason why iface is allowed to be paired only with net to
create an ipset?

I think with feature of skbinfo in every ipset, it should be allowed
to add iface in all ipset. As skbinfo can store tc classes, it might
make more sense if I can pin point on which outgoing interface this
class should be applied.

One direct way of doing could be adding iface in skbinfo itself, but I
dont think its a good suggestion.

So, other thing left is to have ipset storing interface too. Besides,
when I create a tc class, I create it on a known interface, so I know
beforehand on which interface this class is created. So I can easily
specify while adding entry in ipset.