I remember very well what a basegame of an AAA game can be like, I played one back in 2009 and fell in love with it. That experience justifies the hope for me the same can happen again in the future. Toddlers are in fact basegame, they were patched in, so there is no reason to assume a Sims 5 basegame won't have fleshed out life stages as long as they don't rush the release. I want them to take all the time they need to make that basegame a strong and enjoyable foundation. And as for open world, I at least hope there will be large and customizable open neighborhoods (1/3 Sims 3 world, with roads), where every sim in your household is controllable in some way. I just don't think that's too much to ask for.
