It sounds like a decent idea. It doesn't really resolve the problems with calories in vs calories out, though (ie. by and large you still need just as much feed). It also might not be cheaper - lots of meat agriculture largely leaves the animals to themselves before slaughter, which this obviously wouldnt be capable of.

You're also proposing a fairly massive genetic engineering project to get to that point too - I suspect there are many other problems on the chopping block that would be possible if/when we're capable of making those kinds of changes to organisms.

The idea does solve the moral qualms (if we ignore the squickiness of creating an artifical being in a much degraded state from its origin)