Your next milestone of Bumblebee, will be version 4.0! Several people thought the project was dead, but that isn't true.
We will start around May 2016.
For more information, see Github:https://github.com/Bumblebee-Project/Bumblebee/milestones/Bumblebee%204.0
Hopefully a new version will be released not very long from now. Some major issues regarding to the interaction with the NVIDIA driver & bbswitch will be fixed.
Thanks for your patience! Here is already a nice picture of Bumblebee.