What? Why? What's wrong with it?
1) It's backending content that really should be going towards completing the game. The number one desire I see expressed by players is for us to advance the story, not pile on more waifu pounds around TiTS's increasingly flabby waistline. How long have we spent on Uveto? New Texas? Phaedra II is a probe planet we're turning into one of those for no goddamn reason.
2) Even putting aside the amount of time it will take to do, splitting up the main plotline in this manner is a weird decision that I basically don't see the upside to, aside from "MEANINGFUL CHOICES". It means any subsequent event has to take into account that Steele may not have been to Mhen'ga, and didn't engage with Jack/Jill in the manner that they did there. I'm assuming Fen will have the boss battle play out in exactly the same way, but that only makes it even more unconvincing. Of course a reason for access to be opened up to whichever planet you didn't choose will have to be contrived, and you'll be over-levelled for everything there. I don't like any of this.
3) Phaedra II is going to be a post-apocalyptic desert hell world. Meaning players that select it get the wonderful progression of Phaedra II, a post-apocalyptic desert hell world, Tarkus, a post-apocalyptic desert hell world, and Myrellion, an apocalyptic desert hell world. We'd have the same problem if we put it next, but that only hardens my belief that the whole concept is wrong and hasn't been properly thought through.
I see something like Phaedra as something we'd do once, y'know, we could actually say the game is complete. More early game content to encourage people to play it through from the start, that would be great first DLC-type project. As is, it's a collosal waste of time and resources on something TiTS very much does not need. I think that Patreon donors' patience has a limit, and Fen is really going to test it with this.