How about a general upgrade/overhaul to the HUB as soon as it reaches Tier 1?
The Idea would be having the option for the player to rearrange certain characteristics of the HUB as he pleases, for example:
Removing one of the two (or eve both) biomass-generators to swap them out for something more useful, as they do get superflous as you unlock coal-generators.
Bear in mind, I do not have all the ideas, with what construction you could swap them, but one would be an additional rack for personal storage boxes, maybe giving the player a 3 or 4 additional boxes placed over one another (ofc not without some cost to it, maybe a seperate tier for HUB-changes).
Ideas so far:
-Additional Storage racks
-MAM-Extention
-Local Radar Dish - credit @ InspireMe7
-Alternate generator types
-Local Equipment workshop - credit @ Easparte
-Smart-Grid (An energy Substation, giving more information when connected)
Possible Idea for more variety:
Upgrading each module to be more efficient or just be better at what they're supposed to do. E.g: having the above mentioned radar dish installed ad being able to upgrade it to Tier 2, giving it effectively - let's say - double the range.
If this idea intruiges you, let me know what you think and if you have ideas for other modules you can place instead of the generators, tell me in the comments and I'll add them with your credits attached!
Thanks for reading and have a nice day!