Interesting suggestion however has the potential to ruin the gamemode in my opinion.

If players have to option to go into a "ghost mode" and respawn and so get to bhop around the map how would their deaths be prevented upon re-spawning as most maps have an afk player killer such as the breaking floor on Minecraft or the toxic gas on Prison Break and could cause issues with moving player killers such as the orb on Iceworld as you can't see it from behind but still die when touching it.

If godded upon entering "ghost mode" then players can get trapped in places that people should have died before like choosing the wrong portal on Minecraft or if the player were to fall into the water at the sides of Atomic Warfare or the ravines in GoldFever. Likewise a temporary god mode option wouldn't work on some maps either and create problems like the rising water on Amazon that damages for each second you are in it and it's also impossible to climb back up like the breaking floors on Aztecan.

Buttons for secret endings could also be activated by the "ghost team" as I don't think that its possible to blacklist a team from a map object meaning that on maps like Challenging, the secret buttons can be presses by the "ghost team" leading to an easier ending for the runners, the same on Gold Fever if a runner forgot to press one of the signs then a "ghost" could go back to use it and the same goes for the secret buttons on Steam Works and Helix.

The members of the "ghost team", unless coded out, could also have the potential to move physics objects on maps making it easier for the runners like the barrels, breaking crates and platforms or Rooftops or the box, barrel and walls to the next area on Drop as otherwise, unless a living player who has a crowbar comes along, then the "ghost" cant progress through the map hence making the idea redundant as they can't finish the map. If also given a weapon though, then it could also cause problems of breaking the walls on Spy vs Spy or Drop and Rooftops allowing for runners to pass through more easily making it near impossible for a death to stop a prespeeding runner going at 800+ speed. It could also remove the purpose of the 5th trap in the second area in sk_jail as the purpose of the area is that you need to break vents to escape and then it's cutting it close.

Some members of staff after death could be "off in their own little world", as Morgan put it, and not be aware of any deaths breaking rules like trapspam and trapsteal as they are focusing more on their second or more go at the map in stead of patrolling through spectate in an attempt to stop rule breakers for example if somebody were to go into the bin on Family Guy and the only member of staff was bhopping through the start of the map, far away from the person exploiting, then by the time they catch up the invisible player could have already won the map and killed the deaths as they couldn't see the player and hence didn't know when to activate traps.

As Wolfie and Zenternal have also stated, it doesn't appear that there is a working version of the plugin at the moment as the developers not updated their work with to the same version that GMod is currently in meaning that it would most likely fall to Chute or EMP or develop their own, taking what I would assume to be a large about of time out of their days and would probably end up just being postponed until they have time by which point most players might not even care about the plugin anymore.

TL;DR
-Too many problems with maps
-Not a working one already
-Staff may get distracted and not watch over the server
-Would probably take a long time to code a new one

Like I said at the start, this is just my opinion on the matter so feel free to express thoughts on my comment aswell.