For starters, I want to add how much I fucked with the final JLoA roster during Robinson's tenure. Although I prefered the McDuffie run, the roster of Dick, Donna, Jessie Quick, Jade, Supergirl, Congorilla and Starman felt so fresh and cool to me. Really wish it had lasted longer. Also Doctor Impossible was a villain I really dug and wish was brought back/not forgotten/elaborated on
Now on the subject of new members, I've had some ideas over the years. Harley Quinn has been redeemed for so many years now and is the last true DC character to go mainstream, and for that I think that her maybe having a trial run on the League wouldn't be the worst idea ever. A lot of characters who started as or have been villains (ex. Major Disaster, Hal Jordan post-Parallax, Killer Frost, Star Sapphire) have joined versions of the League over the years, and I think Harley should become one of them, especially given how she's become a close ally of Batman over time, like during the Joker War for example. And on the subject of Bat-related characters, I would really enjoy seeing someone from Batman Incorporated join the Justice League (or a potential JLI), with my favorite choice for that being Jiro Osamu. Other characters I'd like to see include a bunch of Wildstorm characters, especially Caitlin Fairchild, since I feel she is the ideal character to preserve in order for the legacy of pre-Authority Wildstorm to stay alive. But, maybe more obscure choices like Flint could work as well.