Just a little poke for myself. There's a fair bit of redundancy with the fact that interwiki links are stored in the cache for each wiki that uses them, but that's all basically duplication when you are sharing the interwiki table.
Just a reminder to hunt through the code. I intend to make it so that when you share the interwiki table, the cache will use the key for that shared table instead of the local one. The data is all equivalent so the idea here is that doing that will reduce data duplication (Can get fairly large on wiki farms), and also improve the speed of the interwiki cache purging maintenance script since it will only need to run over a single database instead of once for each wiki.