you can already play as Fen though?, in earlier versions there was a mode where you played as Fen and just ate everything in your path, And in the most recent version you can go into sandbox and just control Fen.
Right now the experimental version has a lot more improvements and tweaks to various systems, including some new stealth indicator stuff and some animation changes. Won't go too deep on details since all the dev logs cover this. If you're looking for the public build info, just look for the one that doesn't have experimental on it. Last one was in May I believe.
Regardless if it's the public or experimental build it is possible to play as Fen in all the modes. If you're doing it in Pursuit or Buffet, you need to go to configuration and select you're playable as them, though it's possible to still go in director mode on these too. If you don't have these options, then you're playing on the legacy version. Big tell is that the menus and UI are waaaay different, and the current stuff doesn't have as many maps yet.
If you're looking for more updates coming out, I'm not sure when they'll do another one. Got stuff going on with them that they're trying to deal with and not much news has come since then. I'm still looking forward to seeing if this expands further soon, but only time will tell.
Anyways sorry I made this a lil long. Hope this helps answer some questions!