Make it work like elite specs: You can equip a regular trait line instead.
There are a lot of builds (and sometimes professions) which don't have a good elite skill for everything. As a PvE weaver, I sometimes forget that I even have one.
I personally think more core elite skills would be nice, but in the meantime, why not just let us equip utility skills in the elite slot? More gameplay customization options are always nice, and since all of the "new" abilities already exist, I hardly see how this could become gamebreaking.
Just a side thought, might be overpowered: What if we could also equip a healing skill in the elite slot?