Firstly I would carry over the Private Lobby settings to Free Play that are relevant to offline
Allow the settings in Free Play to be saved as they where in Private Lobby's in previous games
Allow AI to be selected from home garage with there custom livery’s (this for example would allow custom races with livery’s particular to event, WTTC, BTTC etc.,)
Allow each AI difficulty to be changed as was in previous games
Allow same make races
Allow Dynamic Weather & TOD changes (might be in, but not verified to the specifics)
Allow to setup championship races, similar to F1 game, selecting several tracks you would race in.