The patches look entirely reasonable to me. The second one needs to be rebased.
I like the idea of stubbing matchjoinsel for now, as well as being careful with operators that may correlate with sort orderings.
The only little thing I can think of is hardcoding it as 2 * DEFAULT_EQ_SEL. While I don't have any arguments against the value itself I think it should be configurable independently. Sadly DEFAULT_MATCH_SEL name is already taken for text patterns. Not sure if it's a reason to rename all the stuff.