Hi Alejandro,
To answer your second question first, we did (Ansible, Inc. and the community).
As for people using it, based on our user surveys we know about 10% of our users run from source, so that is a pretty good amount of people running devel (which will be 2.0 today). Ideally, your playbooks should not need to be rewritten very much for 2.0, however there are some minor changes which shouldn't be too impactful. Right now, we have these documented in the CHANGELOG.md file in the github source, so you can read them there, but we will be moving those to more formal documentation prior to 2.0 final being released.
Thanks!