Allow selection of a byproduct to add a recipe that consumes "All" of it, such as turning all light oil into Solid fuel. Or, more specifically, any of the large number of megamods with Clarifiers or flare stacks, so you can determine how many you need to dispose of excess byproducts.

Additionally allow adding of any recipe arbitrarily, instead of only ones that are required to fill a demand.

Byproduct recipes are possible with the matrix solver, and hopefully one day with the traditional one. The second point is not necessary if you can add byproduct recipes I'd say.

Could you walk me through the byproduct method? Because I couldn't figure it out.

Right, so say for oil cracking, you add the recipe that has byproducts, make sure the matrix solver is enabled, then left-click the byproduct you want to consume. This pops up the recipe picker and it should work as expected from there. See the screenshot below, where it hints you to left-click the byproduct to add a recipe.