It's very important for new sites aimed at some field to attract genuine experts in that field who have a high real-life reputation in that field. At a healthy mature SE site such a genuine expert will typically also have a high on-site reputation. However, for a newly launched site such a person will typically have very low prior reputation because, by definition, their main area of expertise was not already covered by existing SE sites. Thus, during the Area 51 process attracting such a person would be essentially useless to the process even though it's vital to the health of the site.
However, it might be possible to fix this problem relatively easily. Even if the existing SE communities have very few genuine experts in a new field there are still lots of people whose knowledge of that field is more than adequate to assess whether someone is a genuine expert! Thus rather than requiring a new expert to amass their own reputation, there might be a way to let the community notice an expert and thereby increase that person's clout in Area 51.
Is there a good way to make the suggestion in the last paragraph practical? Are there any obvious problems with it? Is this something that Area 51 would/should consider doing? Is there another better way for Area 51 to value real-life reputation?
For a concrete example, Terry Tao was an early adopter of Math Overflow and is clearly of more value to the site (both in terms of activity and in terms of making the site credible in the math community) than a dozen high "reputation" prior SE users. Furthermore, you don't need to be an expert in math research to identify that Tao is a likely huge asset to the site (just read his wikipedia page and note that he's already a big supporter of math on the internet both via his blog and his position on the arXiv advisory committee). Although this is an extreme case, it's also pretty easy to check that people with not quite as stellar credentials are nonetheless credible experts in the field (for example, you can see if the person is a professor at a research university).