They could manage it, though it wouldn't be quite the same as the Citadel, and for it to be more lighthearted in style it couldn't be limited to the Inquisition group we see. Have it be like a formal ball which might somehow suck in many of the previous characters. For example, the Grand Tourney would allow some interesting gameplay opportunities while allowing many old characters to return. Have the chance to bring in Hawke, the Inquisitor, and the Warden/Commander (if alive) all in one go (points if you can even choose which to play). Then bring in a bunch of old characters for fun. Zevran, Isabela, Fenris, Aveline, Bethany/Carver, Oghren, Shale, the surviving Warden character (if one survived). Set it as a backdrop for a meeting between leaders and you have an excuse to bring in Sten, the rulers of Ferelden and Orlais (and a chance, perhaps, for Alistair to participate in the tourney - and the interesting potential to see him face off against Loghain, not to mention the potential for Anora to confront Celene about Cailan), and the new Divine. Could make for a very interesting and amusing series of interactions.