The Instant Teleport allows the Engineer to instantly teleport to his Teleporter Exit. The weapon was designed to allow Engineers to immediately return to their buildings, assuming that the Teleporter Exit was near them, in case they needed to quickly attend to them.
The Instant Teleport was cut from further development because Engineer players had a tendency to place their Teleporter Exits in spots that benefited them more than the rest of their team, breaking the idea of team gameplay. It also eliminated much of the risk of Engineers leaving their buildings alone to gather Metal, thereby creating a balance issue. While trying to solve these issues, the development team "found another idea that played much better, attacked the same problem of Engineers being rewarded for moving out from their nest occasionally, and had lots of other interesting applications"; it is unclear which eventual Engineer weapon or ability this statement is referring to.
The attributes of the Eureka Effect bear resemblance to this weapon.