I think if the members end up doing solo activites it will probably be from seungyeon, to nicole, gyuri, hara, and than jiyoung.
Seungyeon- She could probably do ballads or a light beat cute song. She could also MCing jobs and commercials.
Nicole- Is loved on variety shows and she also is a good dancer so she could possibly do a sexy song for her singing.
Gyuri- Has a good range in vocals so she could probably do any type of songs and she also has acting experience so she could play small roles in dramas or a comedy.
Hara- Could go into modeling again and she is a also a good dancer and if she improves vocally she could probably do a solo or a duet with another member in the group.
Jiyoung- She could probably do commercials and modeling since she has the cute looks and she is very tall.
I think Nicole and Seungyeon have the best chance overall because they seem to gain the the most attention in Kara and loved by many. Nicole and Seungyeon also has a wide variety of talents so they probably have the best chance of making it solo first.