Also with Alex not wanting to release StarSector until its good and ready, a practice I agree with where possible, he also retweeted this post (https://twitter.com/larsiusprime/status/1093391186692329472) (which references off of this (https://twitter.com/RaveofRavendale/status/1093167950360690691)) on his twitter account which feels like leaning towards a dislike or at least wariness of subscription based models for games.
For having StarSector show up on Discord when playing though, I know there are options in discord's settings to link the StarSector.exe or any program to discord's game display to allow it to display when you run it but I forgot where it was.
Rambling about subscriptions/discord here: Spoiler
Personally I would feel the same way, I prefer to own my games and generally try to get products off GOG where possible thanks to the fact that they come with minimal DRM and allow me to use the product as I wish. In fact recently, although I paid for the Obra Dinn on the humble bundle to support the author again I was able to use the GOG version I played to also give the recipient of the gift a working copy without a launcher/platform as well.
As far as I understand it, while a subscription and pay based model like Nitro means that developers can get the 90/10 split, that split isn't guaranteed by the model's existence and can be changed, but it is guaranteed that you're forced to pay a monthly fee to continue to be able to use the games that you had paid for, not to mention if anything happened to discord itself where you would still lose it all.
Really I dislike discord a lot, especially for its lack of professionalism. Its decent for a games forum, but its no wonder that the platform is abused in the way it is due to their design decisions lacking care about how its easily doable and potentially encouraged by the demographics it targets.