Of course it makes sense. For better or worse, Mendeley has a tight following in the among the open-sciencers and associated hipsters, that would pay, donate and help keep the company afloat (see Reddit, even though they were bought by the nasty Conde). Also, going open-source would be a gutsy move, a heck of a PR turn around. It would silence its critics (me included) and it will use the momentum to improve their products and the crappy desktop app.
Imagine the scenario where hundreds of clever people will be buried in Mendeley’s code trying to tweak it and make it better, faster and more reliable. These are very clever people and they work usually for nothing, maybe a like on Friendfeed or an invitation to the next Science Online meeting (let’s make it in some resort location). Mendeley will also have the opportunity to show their corporate clients that they have the community behind them and the community will go wherever Mendeley will go. It’s a win-win, there’s nothing to lose. And all I’m reading and feeding from my sources suggest that’s the differential in Mendeley’s history. They have the opportunity to put their app where their mouths are.
What side of History are you on, Mendeley?