It’s still being worked on, there were some issues surrounding this that need to get solved first.
The main issue being that as long as a linked account is on the same server cluster, things are very easy to deal with. The problem starts when you have an account linked that is on a different cluster – it basically requires that the query gets chopped into a couple of ‘and’ statements, with an embedded ‘or’ statement. The or statements being the player name/server cluster combination, and the rest of the query is the same as it usually is to yank up whatever it is that’s being looked for.
The complication here is that it’s hell on the database, the query as it comes out doesn’t lend itself very well to being optimized and takes quite long to complete compared to the current query time.
But a solution is being worked on, so this feature will appear soon-ish(tm).