

Technically this can already be implemented with Lemmy plugins.
However implementing account age could be circumvented later on since instance owners can edit account age from the instance database. Not an issue for now, but will be an issue later.
Federated karma in the way Reddit implements it can be abused in Lemmy by multiple instances sending each other’s accounts automated like responses. You’re going to need a different metric at the very least.
It’s very easy for any activitypub content to be scraped, all servers practically serve the content on a silver platter to any federated server.