Nebula was a fun character in the original Guardians of the Galaxy, and from what we've heard from her role in Vol. 2, she is only going to be more important. The character has a lot of wiggle room in terms of where she could go from her last appearance.
It seems director James Gunn has been thinking about her own adventures too. Speaking on Twitter, Gunn said he had been considering a solo movie since he first started in the Marvel Cinematic Universe. He said:
I have a few favorites myself, but I agree that Nebula should lead her own film – it's something I've thought about from the beginning. https://t.co/lyPAA6Hyxw
— James Gunn (@JamesGunn) October 16, 2016
To which, Karen Gillan jumped on and said:
— Karen Gillan (@karengillan) October 17, 2016
While there are likely sequels and new characters that would get solo movies before Nebula, perhaps depending on how Infinity War goes down, it would be pertinent. She could be a real anti-hero, which would be a new flavour for the universe.
…I wouldn't get my hopes up though.