The following is based on Tiberian Sun cut content and has not been confirmed by canon sources.
The Threat Rating Node (TRN) was an upgrade for the GDI Adv. comms and GDI Upgrade center. It was Basicaly a extra computer which preformed calculations based on the threat values of units and adjusted AI weapon targeting of player controlled units and structures accordingly.
This means that, for example, a Nod stealth tank would be targeted by a RPG tower over a group of light infantry as the stealth tank is seen as a bigger threat.
If considered canon
It is possible the Threat Rating Node upgrade was phased out before the start of the Second Tiberium War due to improvements made to EVA's AI allowing it to make better and more logical decisions without the aid of extra computers.
During the Firestorm Crisis the TRN upgrades were recycled and kitted with the necessary equipment to allow the commander to call in drop pods. This is perhaps a sign regarding the rushed development was of many of the units and structures being mass produced during the Firestorm Crisis.
The Threat Rating Node can be seen on several custom maps and can easily be made buildable to GDI players by using mods or map edits. Apart from the threat rating not being correctly coded in the .ini files, there is also a problem where, if the upgrade is sold or destroyed, the new threat rating values are not "unloaded" by the game.
The drop pod control plug upgrade graphics are recycled TRN sprites. However, since it is a completely new entry, the drop pod plug can be built alongside an enabled TRN, making for a total of four upgrades.
In the beta of Tiberian Sun a TRN needed to be constructed or the Hunter-Seeker superweapon would not pick targets correctly and was known to attack civilians. Due to the TRN being cut from the game (most likely late in development) it was made unbuildable, creating targeting issues for the Hunter Seeker superweapon. It was not until one of the first patches that the Hunter-Seeker superweapon was edited to correctly operate without the TRN.