I intend to combine my Oracle of Shadows and Light and my Oracle of the Shapeshifters into one big deck, once the latter arrives here. I had the same plan last summer for my Druid Animals and Druid Plant Oracle, but although I really like the card images, I found that I didn't "connect" to the decks the way I thought I would, so I haven't used them all that much since then. I hope that one day the right time for them and me will come - until this happens they are going to live in my big blue tarot box!
Another thing is what Celtictarot mentioned, that you draw a card from another oracle to add to or to clarify a previous reading. I do that sometimes - this has the advantage that the cards can have different sizes because you keep each deck in its own stack. I choose the decks to be used depending on the question of the spread.