I think when they say, "radical changes to the in game world" prior to 2.0 means not changing the layout of the maps that will be used for 2.0, but possibly other unnatural changes to the world around us.

Maybe the same maps for 1.23 will be the same layout, but maybe the black shroud will be somewhat different? La Noscea could spawn even larger versions of creatures we have now possibly as well? Fire, destruction and imperial madness everywhere!?

All I know for sure is, the 7th Umbral Era is here already and when it ends, 2.0 will beckon the 8th Astral Era.

Umbral is the death, while Astral is new life. Umbral is the dark, while Astral is the light. Umbral is the destruction, while Astral is the creation.

I don't know what exactly will happen for sure, but something radically different is going to come to the current maps and when 2.0 (the 8th Astral Era draws near) the new world emerges and Eorzea shall continue living on, as it has for the past 7 eras.