Integration of Mendeley with Elsevier's Scopus and ScienceDirect is very much on the roadmap. The desktop app is going to continue to see more attention. Some great features coming to our next release. We've totally rewritten the iOS app and will be working on an official Android client soon too. Support for win/linux/mac is to continue too. :)
I'm very, very, very skeptical, but this could wind up being a good thing. Elsevier can't entirely make it a "walled garden" just due to the nature of research. Mendeley may not have been able to make their business model work alone. Finally, some of Elsevier's search tools are actually quite nice. Seeing them integrated into Mendeley could be very useful.
I just hope they don't smother/abandon the desktop side of it. Currently, Mendeley is the best cross-platform research paper manager, i.m.o. I'd really, really hate to see them drop linux support, but I'm worried that it's somewhat likely.