Meta Stack Overflow is really the “National Capital”, as mentioned in this bit from the New Per-Site Metas blog post:
Meta Stack Overflow will serve as the “National Capital” where we process feedback not just for Stack Overflow but for the core engine itself — while the smaller meta sites are akin to regional or state capitals.
Given that, instead of setting user privileges solely on Meta Stack Overflow reputation, perhaps there should be a sort of "combined rep" that's used only in computing privileges. Similar to the previously-suggested Why not merge reputation across SO, SF, and SU?, but limited to The One Meta (as suggested by the jjnguy in a comment on that request).
There are a number of possible "combined rep" formulas that could be used, like max on all sites, or maybe some sort of weighted sum. (Please feel free include ideas for such a function in your answer.) Whatever function is used it's probably best to ensure that it cannot be any lower than the Meta rep so as to ensure that existing Meta users do not lose any privileges.
The goal of this feature request is to enable users of all SE sites to contribute on Meta at a level consistent with their "home" site(s).
Here's an example to make it more clear what I'm talking about:
Let's say the "combined rep" is computed as:
max(meta_rep, max(other_reps) / 2) # strawman combined rep function
Suppose we take my existing Stack Overflow and Meta reps, 20615 and 153, respectively. My "combined rep" would be 10307. My rep on Meta would still be (and display as) 153, but I'd be able to do things like show total up and down vote counts or edit tags (two things I cannot do on Meta today) as the "combined rep" would be used for determining privileges.