I think the future of Eclipse+ADT is pretty clear to anyone following the development of Android Studio. It is going to be a second class citizen at best. I honestly hope that it gets killed off completely so as not to pull resources away from Studio development. The lack of clarity on this is a big problem though.
I was a bit surprised to find out how many developers have not yet switched to Gradle / Android Studio. I took an informal poll at a NYC Android Developers meetup this spring and from the show of hands it was about 50/50 Eclipse+ADT vs Android Studio. That night we gave 2 talks on why you should switch to Studio & on how to use Gradle, and I know that gave some people the nudge to switch over, but I was really expecting more people to have switched.
I think the people that haven't yet switched fall into two camps.
#1) Eclipse users. A couple years ago I was at a company that wrote Eclipse plugins, so you can imagine that I'm a pretty big fan of Eclipse. I had never tried IntelliJ at all prior to Android Studio. Switching seemed of dubious value, even though I had heard from a lot of Java developers that IntelliJ was superior. Having now made the switch, I vastly prefer IntelliJ. The refactoring tools are better, and the stability of the IDE is much better. But I think there will be a lot of developers that no matter what the feature set of the Android tools just don't want to learn IntelliJ after years of using Eclipse. I have never met anyone that has used IntelliJ extensively but still prefers Eclipse, but I have met many that simply have never used IntelliJ and don't want to invest the time to learn something new. I don't think there is much the Android tools team can do about getting this group of people to switch other than officially killing off the Eclipse plugin. Some people won't be happy, but you can't please everyone.
#2) Those that think Android Studio + Gradle are not yet stable enough. I think this is the bulk of those that haven't yet switched, and I think this is largely a result of the messaging from the tools team.
My personal experience has been extremely positive. My team was trying out Studio after each release since I/O 2013, and we started getting everything in our app working sometime in August 2013. We switched our master branch over to Gradle and all team members switched to Android Studio in about October 2013. Since then we have been using Android Studio all day every day for production work and haven't looked back. We have lost maybe 2 full days spread over the last 8 months to fixing things after changes to the Gradle plugin causing us to have to rework our build files. That is not a big deal in light of the fact that all of the features in Gradle have saved us a massive amount of time: switching our dependencies to Maven instead of git submodules, package naming, build config, build variants, etc. Perhaps most importantly, Android Studio itself is significantly more stable today than Eclipse + ADT ever was.
But up until I/O 2014 the
developer.android.com documentation was effectively a link to the download page with a big red warning that this wasn't for production use. A lot of people are taking that at face value and not even trying Studio. The "beta" tag and better documentation that was posted will help, but I still don't think it is enough. The impression of Studio from those that haven't tried it is that it crashes all the time, or that Gradle changes all the time (and yes, it changes, but generally it's not hard to keep up with).
Android Studio is the better option for production development today. From what I can tell, most of the really good teams are using Android Studio + Gradle or IntelliJ + Maven already. If it's good enough for the use of teams making apps for millions of users, then we shouldn't be discouraging developers from using Studio. I think larger teams have the resources to try out multiple build systems and IDEs and do their own cost/benefit analysis. Generally the conclusion is that Studio is better than Eclipse/ADT/Ant, and a polished IntelliJ + Maven setup is comparable or better than Studio at this time. But individual developers and new entrants to the platform don't have that luxury. They go by what the documentation recommends, and right now, even with the changes after I/O 2014, I think it pushes people towards Eclipse + ADT.
That is unfortunate because individual developers and hobbyists will benefit the most from Studio + Gradle. The ease of pulling in dependencies & leveraging libraries is highly valuable to newcomers to the community. All of the additional Android refactoring tools & the improved visual design tools makes individual developers more productive and eliminate bugs. And learning 2 tools over the next 2 years is a waste of time for people that are already trying to learn the entire Android platform. I think Google is being overly conservative with pushing the new tools and dramatically underestimating the costs of the current status quo.
I think Google should make it clear that they endorse Studio over Eclipse+ADT for use today. I imagine there was a lot of thought put into the exact wording on the developers site, but "[Studio] will be the official Android IDE once it's ready" is not a strong vote of confidence. In my opinion, in addition to the wording about the fact that in the future it will be the official IDE, it should be clear that it is in use by many developers already and that the Studio is plenty stable (in fact, more stable than Eclipse). The only downside to using Gradle is that the API is evolving and you sometimes have to update your build.gradle files. That's not a big ask from developers in the context of everything else that is constantly evolving in the ecosystem.
And if Google intends to sunset Eclipse+ADT when Studio is "ready", that should be in the current messaging as well. Right now the cost/benefit question is 'are the new features worth the cost of learning a new tool'. If you know that you will have to switch eventually, then it changes your thought process to 'well I have to learn this someday anyway, and I'll get the new features today'.