The touchscreen version of the XPS 15 includes edge-to-edge glass, which is easy to wipe clean, and since the XPS 15 9530 generation that arrived in 2013, that glass has been Corning Gorilla Glass NBT, which is extremely strong and scratch-resistant. So what exactly are you trying to protect against?

And serious question here, how often do you even touch your touchscreen?  I have an XPS 15 9530 with a touchscreen because I thought it would be good future proofing (though if I were ordering one today even 5 years later I'd go FHD this time...), and my Latitude 7480 work system also has one, and beyond the initial novelty factor playing around, I haven't used the touchscreens on either system.  It's just not ergonomic or generally comfortable to hold your arm in the air to operate a touchscreen on a traditional form factor laptop as opposed to a 2-in-1, so I don't even see why they're offered on such systems -- but obviously somebody has a use for them, because the whole industry offers traditional laptops with touchscreens these days.  I'd just be curious to hear some use cases.