A popular character within the team ? Well provided it's not a guest but a female from Tecmo, we only have two options :
Rio : They dediced to give the pink-haired babe her own anime, to include her in DOAP and she has a long history with the team (the large one, Tecmo). Prior to her guest appearance in DOAP, she had never been released outside of Japan. I have no idea if she's SO popular in Japan... would easily work as a tag partner for Zack, based on their affection for casinos, she has a huge selection of fetish costumes designed by the team, and there is a spot under Zack/Phase 4. Plus pink hair.
Irene : She has a long history with the team as well : first lady of NG, later revamped in most NGs, she's the main male character's lover (or something). The team probably thought she was not "strong" enough to be a fighter, she was always seen as the "damsel in distress", but despite this they insisted on giving her some apparitions and a makeover in DOAD... Also very requested. Another blonde ?
I don't think Niki is even popular within the team. I don't know about Ms. Monday, she would be very appreciated in DOA, but I'm not sure there is an expection from the audience for a Yaiba character.