Screen protectors from several companies are already available for sale. Don't listen to the naysayers. Yes it's scratch resistant but it's not scratch proof. It can still be prone to scratches and there is no reason why if you choose to do so that you shouldn't put a screen protector on it.
The Watch is a beautiful object, why anyone would want to cover it up is beyond me. It'll look huge and clumsy on your wrist.
Watches can - and almost certainly will - scratch. It's a fact of life. See it as patina rather than wear. It'll give your Watch personality, make it your Watch; something unique amongst millions of otherwise identical units.
I use it on my smartwatch and glad I do - several deep scratches on the protector. Scratches on screen will be more annoying than scratches on traditional watch crystals, because most of the time the screen is black (unlike analog watches) and scratches are very visible.