My
Biggest disadvantage I see is the total electrical power that would be required to match the deuce compressor's flow rate with an electric one.
Viair compressors are GREAT machines for their designed use (I have installed 20-30 electric viair compressors and air tanks in different rigs; mostly 400C's and 450c's and I have 450C's in every vehicle I own, except for my deuce) However, to match the CFM rating of the factory engine driven compressor (which I am guessing is somewhere close to 10CFM), you would likely need 5 or 6 of the viair 450c units. Each one pulls roughly 20 Amps. That's over 100A, give or take, when the compressors are running. And that is just to match the same flow rate as the factory unit...
There are, of course, larger electric compressors; oasis makes a 9 CFM machine for around $1000-$1500; it draws 180A. No matter how you plan it, I don't think it will be possible to come up with an adequate flow rate for a reasonable current draw. Any time you take mechanical energy, convert it to electrical energy, and back to mechanical again you lose a significant amount of efficiency...
The next disadvantage I see is the reliability and longevity of the system. You are adding several components to the system (electric motor, wiring, electric pressure switch, relays, fuses, etc.) that are all additional failure points that aren't in the factory deuce system.
My advice is to stick with a mechanical compressor. You'll be able to get a higher volume of air with better reliability and lower cost with it.
I personally have found my deuce's compressor to be adequate to run a small impact gun, nailers, air up tires, etc. However, if you decide that you need more, you can always add additional air tanks. You can even place a check valve in line with the feed to your factory air tank, ensuring that it won't back-fill the aux tank in the event of some kind of over-demand, compressor failure, etc.
edit: I wrote this before I saw Chief_919's post recommending the additional air tanks. His suggestion is exactly the same as mine...