In the archipelagos near Stockholm and Gothenburg, for example. There's a list of the nationally financed routes here:
https://www.trafikverket.se/resa-och-trafik/farjetrafik/
Then there are regionally and locally financed routes as well.
https://www.trafikverket.se/resa-och-trafik/farjetrafik/
Then there are regionally and locally financed routes as well.
Most of the archipelago ferries in Gothenburg take around 300 passengers. The smallest one I could find on Styrsöbolaget's site takes 165:
Looking around I found a few listed at https://visitsweden.com/about-sweden/getting-around-stockhol... , for example, https://www.battaxi.se/our-boats says the m/s Alma ("Our fast all-round boat") carries 20.
I also found https://waxholmwatertaxi.com/services/taxi-boat/?lang=en says "We offer Taxi Boat for 1-12 passengers throughout the Stockholm archipelago."
I can imagine some people might pay good money for significantly faster transport + "eco friendly".
Each of those lines has a dozen boats to guarantee frequent service. Including the private options you listed, there are more than 100 boats in Stockholm alone, with 30 passengers or more.
Every city in Scandinavia would likely want something similar; some (Olso, Copenhagen, Helsinki) already have a boat network for commuters and tourists, but every city on that list [1] has a bus network, is around a body of water, and would interested in a non-polluting option.
I’d be surprised if they couldn’t sell thousands for public transport in the region alone — let alone lakes in the Alps, shuttles in the Mediterranean and more.
[0] https://sl.se/en/in-english/getting-around/sl-service-networ...
[1] https://en.wikipedia.org/wiki/List_of_urban_areas_in_the_Nor...