platyping
Sleeping Dragon
It uses a simple function "canEverResearch" to decide whether to display or not. This function only checks the tech itself and not the whole tree leading to it. To do what you want, is technically unfeasible due to the number of checks. To decide whether Future Tech is researchable or not, you have to check every single tech of your 1000+ techs that leads to it, which will just slow down the tree. And of course, every tech in the future era will come with another 900+ checks each.
Rather than making your players suffer from a slower tech tree by adding all these checks, it is easier for the modders themselves to make all those techs you want to hide, disabled, rather than just disabling the initial tech.
If you don't want to edit every tech xml, there is a CannotResearch function in CvGameUtils for that purpose. Just create a list, if it is in the list, disable.
Rather than making your players suffer from a slower tech tree by adding all these checks, it is easier for the modders themselves to make all those techs you want to hide, disabled, rather than just disabling the initial tech.
If you don't want to edit every tech xml, there is a CannotResearch function in CvGameUtils for that purpose. Just create a list, if it is in the list, disable.