Overview: I'd like to have the potential to include multiples of metatags in the search field.

Why: While you normally only need one result, thanks to range searches (<10, >=100, 1..5), both inverse ranges (<10 OR >=100) would require multiple metatags. Similarly, if you're trying to compare favorites between two users, you would need to use separate metatags (fav:foo fav:bar for images both users favorited, or ~fav:foo ~fav:bar for images that were favorited by either).

What would be affected: The posts, as well as the coding behind how searches work to get metatags to have the same functionality as regular tags.

I guess you could always use exclusive metatags (They work!) for the inverse ranges, but that won't work if you've got two exclusion ranges, or two normal ranges.