Currently, the Area51 commitment process seems to be based in large part on the rep that is used to commit to a proposal. This is somewhat understandable: so long as many of the areas of interest are centered around similar topics to existing StackOverflow-based sites, this is a practical way of ensuring that the users who are committing have demonstrated some tendency to ask and answer questions on these sites.
However, I feel like there is, to some extent, a bar here that it is difficult for SE-style sites in new areas to really get started. Take 'Fashion', for example: Very few existing SE sites are likely to have a significant amount of Fashion related questions or answers, and as such, the users who are ideal to help make the site succeed tend to have very little reputation.
The current Geographic Information Systems proposal is not particularly different; there are relatively few questions related to GIS existing on the current SO site, and they are generally lost in the noise. (Even when looking for them, I had some trouble finding them.) This doesn't necessarily mean that this topic would be ill-served by a SE site; merely that the community isn't well-served by the existing sites.
Yet despite having double the number of committers of the next most-committed project, the project is less than halfway through the 'progress' of the commitment stage; the users who are committing are low rep users, many of whom have never used StackOverflow to ask or answer questions. (Some may also be in a situation like myself where their existing rep is tied to other 'StackExchange-1.0' sites, but I'm willing to accept that's probably the minority.) The 'web development' proposal, on the other hand, is proceeding nicely through the commitment process, because many of the users are well-served by the existing SO community.
With no way to generate rep (other than flooding unrelated sites with questions), how can a community gather up the rep needed to progress out of commitment if the topic of interest is not well covered by existing Trilogy sites?