Let's be real. Nobody's going to equip 10 abilities and deal with a random 5 being selected at level 50. Everyone is just putting together a set of 5 abilities that they know they'll always have. However, people do have reasons to swap out some abilities for others based on the recipe.

So how about this:

Instead of pretending we have more than 5 slots how about we actually get to equip abilities to all 10 slots, and be given a quick interface with which we can select which of them we want to use before each recipe with the previous selected options remaining as default.