My perspective is following:
No one has been able to move to the develop branch and I don't see anyone will.
AFAIK BAR is the only game working on moving rendering to GL4 and despite the efforts we are far from completion yet: It's the reality that the current accrued assets such as widgets will stay not migrated probably for years. Therefore I see no value in releasing the develop as any numbered release. At least in the current circumstances.
My initial strategy was to enable optimized GL4-like rendering capabilities via Lua API. This task is more or less completed. The new API enables very efficient rendering submissions. See
viewtopic.php?f=13&t=43644 as example.
The refined mid-term strategy is to replace rendering subsystems of the current engine with GL4 code one by one. The code from the develop might be used as reference implementation where applicable. You probably have seen prototype class implementation of GL4 UnitDrawer:
download/file.php?mode=view&id=11377 that enabled 10x FPS improvement. The plan is to continue this route and integrate such changes one by one while keeping the rest of the code intact.
I propose to integrate the current BAR branch (~280 commits ahead of 105) as 105+/transition/106/whatever the name you like. Currently it's 99% if not 100% backward compatible with 105.
Moving on I'll be replacing various drawer subsystems as outlined above. Such changes will require adjustments on game side (for example GL4 unit drawer will require changes to custom unit shading framework obviously), but the scale of doing such changes should be manageable.