Well there are blogging platforms for the fediverse (ie they federate) I forget their names but in it sure WriteFreely is one.
Beyond that, Wordpress has integrations now with the fediverse which federate as user accounts. It seems to work ok, in that I’ve seen blogs appear in mastodon. But one point of friction I think is how comments are federated. Maybe it works fine but I’m key sure they’ve made a choice to not federate comments from Wordpress to mastodon so there’s context collapse.
Otherwise, the idea I’m thinking of hasn’t been realised yet AFAICT. TBF, it would probably require more than a front end for lemmy, I suspect some backend features would be required too. Nothing too big I’d think. But alas no. Still think it’s be cool!