I believe you're asking for a way to prevent items from getting burned in lava. This could be easily added, but I personally think it should stay the way it is. You can also modify your farm to save any spawners from getting burned by adding hoppers under the water; the water hoppers pick up anything that falls into them, and the lava hoppers will pick up IG drops. They won't be mixed together because the IGs won't take damage until they hit the lava, which is past the spot where spawners would drop.