Is this within the realms of possible?... yes certainly, I've done exactly what you're proposing to do. How easy is it to do? It depends on the spec and age of your car versus the spec and age of the S5 seats you procure. Ideally you want to keep them as close as possible age wise (by age I mean match up pre and post Facelift whichever you have). It's not a deal breaker but it just makes it easier. The other thing to think about is heated seats. Do you have them? Because the S5 seats will. As regards the electric, if you've got electric lumbar support then the fully electric S5 will just be plug and play. Might need to adjust the fuse to deal with the extra load (right hand side / drivers side). There are posts on here that say you need VCDS component protection removal and all that but it's more than likely if you keep things as close a match as possible you won't need it (I didn't). You might need to do a little bit of customisation, I had to change my airbag connectors but this was straightforward. Best of luck with the mod.
