I believe $5200 is with the 2022 price hike, unless there was an official announcement in the last few days and are going to increase it again in a few months. Last week I noticed the price hike of the 833 go up from around $4700ish from memory, as well as all other 8-series and MixPre IIs getting price bumps. In a thread I brought this up, and some said chip supply seems to be one factor, and some brought up new owners potentially trying to increase profit margins.
To add my thoughts on the 833 plugin. (Coming from someone who is only dreaming of owning one right now) It seems as though this is just taking advantage of shared hardware between the 833 and 888, with some development to adjust to the 833 controls. If both of them have the same recorder chip, and this is not a massive R&D task, then this seems a bit overpriced, for $400-500 I could totally see it.