They have been working on and off an official Mod API for a while. http://www.eurogamer.net/articles/2012-02-29-mojang-hires-bu...
But this has nothing to do with monetizing servers, which is the point of the post.
But this has nothing to do with monetizing servers, which is the point of the post.
How does this relate to the monetization issue? Well, from a technical perspective Mojang seems to be phoning it in these days, in terms of Minecraft.
The console and mobile versions seem to be getting regular love while the core PC version has been in near-limbo for most of 2014. The plugin API, promised for well over a year (and I suspect over two) is still nowhere to be seen. Notch, creator of the game, isn't even involved with it anymore beyond the occasional "voice from the mountain" posts such as this. While I'm sure they have some talented people touching the code (e.g. Jeb and Dinnerbone), the focus and drive appear to be missing.
So when I hear about the EULA debacle and the half-assed cloud of confusion and conflicting messages coming from Mojang, I'm not surprised. I like the game, but have no idea if anybody's really steering that ship with a particular destination in mind.
Draw your own conclusions.
The 1.8 update, currently in development, has added features, but it has mostly focused on refactoring and cleaning code. For example, they recently rewrote the entire block id system, removing numerical ids and instead using namespaced identifiers. This will allow mods to coexist rather than try to claim the same block ids.