A few things...
Modularity would be great, but the big thing standing in the way is you can't introduce completely new objects at run time. In other words you need to be able to reference things that may, or may not exist.
More assets sounds like a good idea, but that can lead to some bad things you find in all asset stores. Usually they wind up being the front end for someones portfolio, in that they will add cheap graphics, but they will be largely incomplete in order to get some more work.
Secondly, art is not reusable, in other words, a Pacman platformer is not a good idea.
Lastly, multiplayer really must be server based. You can't do reasonable security in p2p, and a database is necessary for a ton of basic features.
However, a server based game is a different animal, and you have to do several things differently, the foremost being actual code.
Im not even going to address svn, as that would have to be a layer added on after all those other things are taken care of first.
Edit:
I will say I absolutely hate working on other peoples event sheets.
There's usually a few unneeded "for each", and I hate it when people put multiple conditions at the top level