I have a suggestion.
Im a currently trying to build NYC realistically. An issue I see is that there are not that many rescues for the number of stations in that city.
On further research I found that the Ladders carry hydraulic tools (please correct my if I am wrong, but even if not I would think this still could be realistic).
So my suggestion would be a combination of a platform truck and a rescue.
As we already have a Quint and a Rescue engine in addition to countless dual purpose units I think this would be a realistic addition to the game.
Feedback is of course welcomed!