I was thinking more like, you need to re-evolve the whole lamina to re-juggle water conductivities in mesophyll, cuticle, vascular bundles and what else is there, to maintain water flow throughout the leaf. And all that newly made sugar which would have to be dealt with (don't remember how it influences osmosis.) Which means different auxin fluxes, which would rebuild the rest of the body.

But yes, of course it is at least that difficult.