The purpose of the GSC research chain is to open up a GSC-playable path.
The idea being that you capture some actual genestealers, and if you have more than X in captivity for Y days (scripting dependent, might not be possible to implement), or if you research a particular topic down the chain (due to the scripting limitation) - then the genestealers "escape" and infect you and you enter the GSC path.
Example, the GSC path research topic could become available after researching all the relevant topics in the chain (6 or so) + Having researched a live Genestealer. This triggers some event pop ups + makes certain gameplay options available.
-> Opens up soldierTransform options to infect your current soldiers (bust in HP and some other physical stats).
-> Opens up some Hybrid-ization upgrades (surgery) and genestealer recruitment options.
-> Turns off the GSC hostiles/missions from generating (might not be possible to make existing enemy GSC bases disappear in OXCE, but random missionScripts can be shut off).
-> Activate GSC flavored eventScripts and research options to "infect" the world and get resources.
-> Activates the alternative final mission that Chaos Path gets, but GSC flavored.
You'd still fight Chaos/orks etc, and maybe activate the Inquisition and fight those.