Gotcha.  I think that is a slippery slope.  There are other oddities we would need to enforce:

* Can only apply `sort` when `fl` is set to unique id, otherwise must return an error (basho/riak_search#86).
* The `sort` parameter must be ignored (basho/riak_search#136).
* Possibly other weird things...

I think Yokozuna should fix these issues rather than reproduce them.  Having these issues is not a feature on which anyone should be relying on.  E.g. I don't see why someone would complain because something that used to give them an error now actually works.