I know that if EA were to introduce a concurrent online feature the devs would spend so much time there, that other features would be stripped to nothing. There would be many limitations online play would impose. Also when the game falls out of support in the future, the game would become unplayable because it has lost the online feature. Keep it offline and go all out on in game content.
A reasonable suggestion for online play is to have friends' sims visit your house but they show up as an NPC and does not have a concurrent play aspect. I don't know how feasible this is, but this could be nice as long as it doesn't limit the game in other ways.
