Shimano DA9000 polymer cables
Couple of points:-


Firstly, yes they are compatible.
Yes they do shift better of standard cables, this is due to cable drag. Cable drag is basically the friction between the inner and the outer. This friction causes slower and less accurate shifting. The polymer on the inner decreases the coefficient of drag between the inner and outer, this increasing shift performance. Now that seems like a lot of marketing BS, but having used both, I would now always opt for the new polymer cables.
Next to having to scrape the polymer off, this is easy and honestly, just clamping the cable breaks it away. Its pretty fragile stuff.
Next to your point of using WD-40 to keep things running properly, WD-40 acts as a degreaser, this actually strips the silicone grease off, and will dramatically decrease shift performance and cable life. You would be better off not trying to lubricate the cable at all rather than using WD-40. Lubricating the cable with a touch of silicone grease however is well worth it. When I clean or service bikes, I put a touch of silicone grease where the cable exits the outer at all points. This helps two fold, firstly it stops water/dirt getting into your outer, secondly it will work its way into the outer and help keep them lubricated.