I saw Open Startup List this morning and thought that this might be the start of some standardization across open startups. That could transform this movement into something a little more serious. It could, in effect, create a new type of "public" company - companies that are transparent with key indicators but still independent. The impact could be huge on how funding and investment work.
Comparable figures across different startups in the same markets or industries would also be awesome for understanding markets and how growth work. Eventually, these figures might give other startups the ability to benchmark and understand how they are doing compared to other similar startups.
Starting with an aggregation of the different data available might be a good start, perhaps with some data visualizations. You might be able to influence what some of the key metrics companies are exposing are. You're probably already thinking about putting together more detailed guide for how new startups could start exposing their metrics. That could easily transition to a standard set of metrics these companies should expose.
If you could standardize what an Open Startup is, that could really change the game.