GSM-R is a British rail system that could be put into Train Sim World 2 other than Train Simulator 2021.
I don't think the GSM-R is gonna be in TSW 2. It doesn't really have a purpose other than Logging in and contacting the Signaller.
In it's simplicity, when you reach a red signal and need to contact the signaller, the game could prevent you contacting the signaller without it turned on. It could also be used as an important tool to deliver messages if we ever see randomized/dynamic events introduced to the game. All of these little things contribute hugely to the simulation and immersion. After all, we have switches and dials to control train heat, air conditioning, hot plates in the older BR locos. Do these actually do anything... No, because the player cannot perceive heat or air when playing. But, they do add to the simulation, as would GSM-R.