They'll probably focus on creating custom blocks and items with their plugin API via command block scripts, which is why all of this mess was added for block and item registration, block states, models, etc. Potions would be less important to be able to add when users can't really code in custom effects (at least not yet). Same with entities, biomes, enchants, etc. So why bother updating that code?
Mojang's priority is still vanilla, with existing modding probably factoring very little, if at all, into their decision-making process. I've said it before, but we wouldn't still be dealing with obfuscation if modding was anywhere near the top of their priority list. I can't think of anything that was ever added that was meant specifically for the sake of the modding community, not even recently when they left in a tad more obfuscation data related to inner classes and such. Even something like launchwrapper; yeah, it's improved modding to some degree, but more importantly, it allows them to tweak older versions to run in their launcher which they couldn't do previously, while simultaneously providing a way to mod Minecraft that lets them officially frown on distributing JAR mods nowadays. There always seems to be some greater benefit to them. And I don't hold any of it against them, it's not in their interest to do us any favors, and I'm not forgetful of the fact that they don't have to update the game at all and could have cracked down on modding a long time ago. Though I don't confuse a lack of acting against something as approval of it, either.
So, just as it's always been, it's up to the community to make the game easier to mod. Luckily we have some competent people working on Forge again so I'm hopeful of it making strides to improve this kind of thing, just like it used to.
