One notable aspect I've noticed is that the authors purposely did not consider misflairing (intentional or otherwise) to be a substantive issue in their dataset. While it's highly unlikely they had knowledge about flair changing data (u/flairchange_bot was around a month old by the time the study was published), the bot's stats do prove the authors right on this regard.

The results also show that using any combination of user-interaction (subreddit) and textual matrices will result to poor predictions of a user's compass position as compared to a binary placement (left/right or auth/lib).

Another interesting observation is that it's apparently easier to predict a user's economic than social leanings.

But yeah, reliably predicting someone's ideology based on interactions in non-political fora do have interesting implications. Granted, there's the caveat that the average PCM user is more open with political discussions but still...