I mean, I REALLY want the Geothermal Energy plant back ;-;
But anyway, there is still great potencial (and time!) for one last DLC to release before Tropico 7 comes out

There are various buildings from previous games and their DLCs that could fit so well in Tropico 6. I first think of the Geothermal plant cause it gives a good reason to build near volcanos, but there is so much more. In Troipico 5 the SuperComputer was always a favorite of mine too and the Fortress could be an alternative to the towers, with a new upgrade on each era and maybe having more health but less damage, to balance things out

That is, of course, without even saying anything about brand new buildings too