AFAIK, currently we can compare MySQL vs MariaDB as:
MySQL MariaDB
5.1 5.1 / 5.2 / 5.3
5.5 5.5 (including MariaDB features from 5.2/5.3)
5.6 10.0 (based on MySQL 5.5 with backports from MySQL 5.6
and features from previous MariaDB versions)
5.7 ???
The first question for us is what version number will you use for a newer version based on MySQL-5.7. Another question is if you plan to port all your work to the 5.7 codebase or if you'll keep working on the current 10.0 codebase and do backports from 5.7 (like you did for MySQL 5.6).
A second question is whether you still claim binary compatibility with MySQL[1] and how would you compare the latest versions of MariaDB and MySQL (10.0 vs 5.6, 5.7).
Thank you and regards,
Jorge Manuel B. S. Vicetto