Well you could use a mild metal polish (Al is soft so a mild polish should work, highly abrasive ones will just scratch it more), but the problem is that you will then probably have a very shiny unoxidized spot that will then not match the rest of the back, so unless you are willing to polish the entire back this probably isn't a good idea as mentioned. The only other option I can think of would be to get some metallic color paints at a hobby store then mix them together until they match the color of the iPad and then use a very fine brush and fill in the scratch with the paint...the hobby store can help you choose the right paints for metal. Kind of like how we used to remove dust spots on our darkroom photos in the old days...if done right the mend is invisible...but I never could do it right, best to keep dust off the negatives, lenses etc. before making the print 🙂 .
As to covers they may or may not disguise the scratch, but then you will have a cover/shield on it which may or may not be a look you like. I do wonder, esp. with the thicker ones, if they will make the iPad more sensitive to heat since it is passive cooling only it may not take much to cause it to overheat...or maybe not (time and user reports will tell on this)...since the ambient temp max spec for the iPad is 95F this may be a concern for some.
