Is it even worth mashing in at your desired saccharification and then do a decoction to mash out? Can you get the appropriate mellanoidins from this type of mashing schedule that you'd get from a protein to saccharification decoction mash?
No, since the mash-out decoction needs to be thin and conversion has already taken place, you won't get the intended benefits. For a single decoction, you really have to go from a protein-related rest to saccharification or dextrinization. You don't have to go from a full-blown protein rest, though. You can go from low to mid 140s°F to 158°F.