Now that the show will have a lot of heroes/villains making an appearance on the crossover show (especially new ones like Jonah Hex according to show-runner Phil Klemmer) [DC's Legends of Tomorrow](tag:2937021) is an anthology series (a la American Horror Story) and will featured a different cast for next season and this is my future line up for the newest members in season 2:
Now that the episode in which Matt Ryan guest starred to reprise his role as the P.I had received a lot of positive ratings, he would be perfect as a member and possibly his show will come back sooner now that it take place in the Arrowverse
Even Thought Many Huntress fan's dislike her due to becoming an Anti-Villain but that's chances that she will return on the show since the last time we saw her in season 2.
Now that an Easter Egg of the Gas Mask wearing hero was released on Legends of Tomorrow social media along with three other which may see him soon and he could qualified for the role as an member.
Hawk and Dove
Now that the Teen Titan's pilot (in which they're going to be member's) supposedly got cancelled that's chance they could replace The Hawkcouple as the battle couple for the next team.
Franz Drameh (the second Firestorm) say in a interview that he would to see Virgil Hawkins on the Arrowverse especially as an future member of the team i do like to see Static making an appearance too.
With Valentina Vostok making an appearance at last week episode it's possible that we get to see The Doom Patrol including BB and have him as an future Legend.
With Megalyn Echikunwoke reprising her role as the animal lady in her first live action appearance in Arrow maybe she'll get a shot for next season.
With the return of Colton Haynes as Roy Harper aka RA on Season 4 we would love to see him more again in future season especially as an possible candidates for season 2 we miss him so much.