There is no set timeline for merging the 3.0 branch into the master branch. We want to make sure everything is working properly before moving forward. We do have plans to support reading 2.x earth files and to continue support TileSource plugins; these things are still in the works.
The 2.10 branch will remain for those who wish to stick with the existing API. Bug fixes and minor upgrades will occur on both versions as long as it's feasible.
All questions are welcome and we appreciate any constructive feedback!
Thank you and enjoy.