I've noticed for a while that quite a few of the major contributors to any given one of the trilogy sites are active, to some degree, on all three of them. And since the beginnings of the beta phases of new Stack Exchange sites, I've noticed the same thing with those: there are quite a few people who are active on one or two of the new beta sites (or more?), as well as the original trilogy.
This has led me to wonder about the possibility of cross-site badges, which would be awarded for a certain level of participation in multiple Stack Exchange sites. For example, there could be a hypothetical badge awarded for visiting each of a particular set of 3 different SE sites every day for a 15 day period. Or one for achieving 200 reputation on 5 or more sites. Or one for having an answer with +10 upvotes on each of 3 or more sites. (I'm not saying that these would be good badge criteria, just trying to provide illustrative examples) Basically, these badges would reward people who don't limit their activity to just one site, and hopefully would encourage existing contributors to one of SOFUetc. to branch out and look for new Stack Exchange sites to get involved in, thus strengthening the network.
Of course, the obvious problem is, which site(s) would these badges display on? Would they be associated with all the sites they were earned for, or would they display on every site at which that user has a linked account? And I have no idea what sort of problems could arise on the development side - there isn't really any other feature (that I know of) that really integrates different trilogy sites like this, so I can imagine it might be a lot of work to implement such a feature on the backend. Bottom line, I can certainly think of reasons why this might not be a good idea. But it is an interesting idea, so I thought it was at least worth bringing up for discussion.
So is the cross-site badge idea something that people would be interested in, if the implementation details could be worked out?