Another possible model to consider in part is one that a few of the lesser known, in most circles at least, use----which goes something like "Paid members get access to the latest major features 6-8 months in advance of free users, beta-level and otherwise." So, it becomes something of a choice as to how far in the past you want to lag behind versus being able to deal with fresh and functional things.
Reaper's model seems to have served it well given the years they've been at it though, so in the end I suspect one can't go terribly wrong at using a version of it with some relevant tweaking given the software/hardware realities of a game engine/dev program suite are different versus a DAW and the like.
An answer needs to be arrived upon promptly though, as the other solutions from the various other outfits from small to large are chugging along and thus Scirra is going to need to act with agility and speed regardless of which path is trodden. This whole Molehill thing finally happening on the Flash end alongside Unity throwing in a bit with it is huge alongside the JS to C# stuff and whatnot.