No, especially if PS4 became console leader. But EA might drop support but who cares about EA? I don't think most developers even want this to happen anyway

Doesnt make much sense does it? They would drop Sony cause of no used game anti-measures and would go on the Wii U wich has none? I think the chances of that happening are zero. EA will just release their games on the Playstation. At best they give exclusive content to the Xbox version if that was true. Still not worth it in my view compared to the lost sales.

No, it means 3rd parties will just continue with the DRM they have in place now

First off, I liked to say I do not agree with DRM. However, If Xbox One is going to have this feature, and Sony does not implement something similar, it could be detrimental. The reason being, I believe Sony would lose 3rd party support. Why would game developers, specifically EA, not develop for the PS4 and lose all that potential money? I think it all comes down to install base. Some believe if Sony does not implement DRM, this will be the console that gamers support. What if games like: Madden, NBA, Fifa, and many more games never make it to the PS4? These games are ruled by the casual market. Selling millions upon millions. So my question is, wouldn't the casual gamers just move to the Xbox One if those games aren't offered on the other systems? Thus increasing the Ones install base, and developers really wouldn't be losing money because it would average out from the install base.

As long as Sony sells similar or better console numbers as Xbone 3rd parties will not ignore a substantial source of revenue, even if no DRM means slightly lower game sales.

No. If 3rd party publishers stop supporting the PS4 they'll end up "killing" themselves along with the PS4.
Sony and Microsoft have the final say in terms of DRM. Publishers are picking sides but they won't abandon the other.

no, because PS3/360 games sell millions upon millions.