Let’s say you have two accounts, but don’t like the idea of splitting your play between separate accounts. You’d want to be able to merge them, wouldn’t you?
That being said, it would have to be regulated so that users must ask permission first, and the ranks between the accounts must be within a certain range of each other, ±3 probably, otherwise you could just merge a sandbag account with your main one. But other than that, it would probably be healthier overall to avoid unnecessary multiple accounts if possible.
I assume OP was referring to online-go game site, the above link is concerning only discourse - the software that our forums - not game site - run on. And as we link forums accounts with the online-go.com accounts, we cannot merge them here either, even though Discourse has the function.
I am afraid merging accounts is unlikely to happen anytime soon. It would cause a lot of potential issues and confusion with very few possible benefits as far as I am concerned, and would be a lot of work to implement into a code that was not originally written with this possibility in mind. Not that it is my decision, but I would call it an educated guess that such a feature will not be avilable in the forseeable future, sorry.