I would like to see a tech option that opens the option for a faction to reverse the Terraforming direction in the last ring of the science tree.   For instance, turning an arid planet into a desert as the United Empire. 


The system upgrade seems to be set up such that a level 4 system could provide up to +24 resources per pop or +flat bonuses per system.  


With the per pop style, you want fertile systems for the most total FIDS even as Riftborn.   With the Flat bonuses per system, you may want tier 5 planets for more focused outputs.  


As the luxury goods your empire has access to drives my choices for system upgrades and my game strategy, having the option to adapt your empire in this fashion would provide additional strategic depth, and also allow people to transition planets (via much expenditure of industry) from Atolls to Forests for instance.