The reason she was withdrawn by Calmac in 1981 was that she basically needed re-boilering and a lot of other mechanical work done which coincided with massive public spending cuts by our friendly political party with the blue rosettes. Not only that but she was an anachronism within the Calmac fleet at the time, operating solely on the loch for tourist purposes, being a paddler and being steam powered.
She's also not owned by the council and so why would she receive a subsidy?
Loch Lomond has an enormous tourist catchment and Maid of the Loch has the ability to offer a service that the existing boat owners cannot provide, especially considering the size of their vessels (very much smaller).
High end dining cruises as well as jollies up and down the loch for punters of different means is what I believe is envisaged and I'm sure she shall be successful at it. The length of cruise will likely be longer than the current operators, many of whom seem quite positive about the Maid's return to service as she'll be an attraction in herself.
You only have to look at comparable operations on Windermere and abroad to see how it can and indeed will work.