SVN is totally out imho, its should be used as an active development tool, not a showcase one. I reckon most mod auhtors do not want to risk being at the mercy of a central site going down, at least i am very opposed to that idea. At times when SMF site has been down, the Tinyortal site and others, has served as small news beacons during that, not hindering the slighest the development cycles and support there.
But getting big as some 3PD sites for Joomla for example is quite possible I guess, all it takes is people willing to take the plunge. How to make that easier I cannot say really, using the "supermod" way is def. out, as it presents as many problems as solutions, if not more
I guess its also down to popularity and getting more serious third-party developers on board - there I think SMF still appeals more to the beginner/home crowd than the business crowd. Of course SMF is well beyond mature enough lol, its just that we have a target audience that we serve very well - but its not the same as for example Joomla serves. PhpBB has the edge of being more known and longer in existance, same for the paid ones - which in themselves lend quite a bit of credibility just in the fact they cost money
We have the advantage of being free, have a powerful template system and a plug-it-in system for mods. Thats our main assets but again advancing 3PD needs something more I guess...Recent talks elsewhere about themes for example, being possibly in violation of SMF copyright, DOES not encourage others to bet on SMF. There we need to clarify and not speculate, NOT feeding the rumour that *everything* is in violation of copyright.
Just the fact that mods/themes on 3p sites thrive already should be enough.