'15 Ford Fusion eating coolant

[zzyzzx]

My simple brain says take the block to a machine shop and have them TIG weld 90% of the cooling slit and then resurface the deck and reassemble with a new head gasket. Essentially you'll have the updated design now.

At least on an Escape or Edge with the 2.0 (I'm not sure if a Fusion had the towing option available):
I don't see what that wouldn't work, especially if the vehicle has the towing package with the upsized radiator. I have no idea what other parts might besides the radiator would be different for that engine with the towing package.

I also wonder if the block doesn't need to be decked, is there a JB weld type of product that you could use to infill the slot.