A good solution could also be if they'd preserve the old assets and leave them in the game. So then there would just be a new asset that is essentially the same building/thing, but is just the new version. That would leave the old assets exactly the same and would cause no issues as far as I'm aware... That is probably the route the devs will go. But maybe they have another strategy. However they do it I'm sure they have thought of this problem as they are aiming to keep mod support to their best capabilities.