I don't think there is anything to be worried about for song rights. The green manga seems very beloved by the music industry in Japan. In case some of this didn't get mentioned here before...she got an official spotify playlist early on, she got to keep a lot more music references in the print version than people expected, a merch collaboration with the Nirvana anniversary album, Mitsuki singing Creep on the Drama CD, they arranged for her to meet Beck, and soon the manga will have an officially released soundtrack with a lot of well known bands.
Currently the manga has a storyline that doubles as a product placement for a real music festival in Japan. They are basically lockstep together at this point. Domestically I could see an anime or live action getting enough music licensed for it to feel right because everything is leaning towards the industry wanting it too. If there are issues down the road for a US release for example... that wouldn't be stopping them from making an anime or live action if they really want it. They'll be making it for their domestic audience.
I think an anime or live action wouldn't be difficult to adapt. They might need to add some connective tissue, but this is a coming of age slice of life series. It's not like it's trying to add content to a difficult to understand avant-garde scifi manga. There's not much they can mess up if they just hit the major beats. Needing to add some school, cd shop, and home scenes that help flesh out their inner thoughts more in a visual way vs manga shorthand seems a reasonable use for extra time without changing the story significantly and there's enough there for one season with three volumes if that's as far as it goes.
Funny enough, a fan who is an animation student made this cute animation short this week and it has me really wanting an anime some day even more than before. I love it when a series I like attracts talented fans for fanart.