The idea is to add the possibility of building a space elevator on planets to deliver items to space platforms (and possibly from platforms). This would diversify the solution of logistical problems in modded playthroughs, and overall would look like a cool addition. (Although there is a space elevator in the Space Exploration mod, it works on a different principle and cannot be added separately to the main game, but I would like to have a separate elevator to complement the modpacks and the main Space Age).
Naturally, strict requirements for the construction of a space elevator will have to be introduced for the game balance. For example, several stages of construction with excavation of the foundation, etc. as in the Rocket-Silo Construction mod, a limit on the number of space elevators (1 per planet, or no closer than 2000 distance to the nearest elevator for example), the high cost of construction (including unique resources from all 4 base planets), the constant maintenance using those unique resources and constant draw of large amount of energy. All this should make building an elevator impossible in the early and middle game (also tech research level cryogenic or promethium), but possible in the late game, which should slightly reduce the benefits of using it.
Codewise, I think the space elevator could work as a fast, free (or almost free) rocket silo. It will be good for the mod to have compatibility with other mods for using it in modpacks (the ability to install with other mods, the ability to use resources from modifications).
TLDR:
Space elevator building, which is expensive and constructed in several stages
Space elevator can transfer items to (and maybe from) space platforms
It is hard to get and maintain, but cheaper and faster to operate then launching rockets
Codewise can be just a free and fast rocket silo, or maybe something else
