Based on the comment, I think that what is wanted is a little different than what people are assuming.
First, it sounds like there is a desire to implement enough of the Mastodon API that various mobile Mastodon clients can connect to kbin.social and interact with that side of things. I have no idea how difficult this would be, but I suspect that it would be an interesting undertaking.
And second, unrelated, but it came up in the comments, and I think it would be an excellent idea, there is definitely a desire to implement a Mastodon-like way to export and import enough of your account information to easily migrate to another instance.
In my opinion, there needs to be an option that can both import and export a fully Mastodon compatible format, so that people can migrate from Mastodon to kbin, and can migrate back from kbin to Mastodon, at least for stuff where that makes sense.
At the same time, I am unsure if that format would be sufficient for everything required to migrate from one instance of kbin to another, or between kbin and lemmy.
And given that last point, it should come as no surprise that I think that if another format is needed, or even an extension to the existing format, that should really be coordinated with Lemmy, so that it is easier to move around the entire ecosystem.