While "software as a service" was a big paradigm shift, because that moved the physical boxes out of companies' own data centres, MaaS appears to me to be a massive gimmicky buzzword to describe the rather simple problem of integrating the booking and payment of multiple modes, something which people don't find unduly difficult to do manually anyway.
After all, unlike software, all transport that isn't walking, driving or cycling is already a service.
The other aspect regarding payment (the ability to subscribe to the transport service) also already exists in the form of season tickets.
The last aspect, shared demand responsive transport, has its own little niches where it sort of works (paratransit/community transport and very rural areas) but other than that people keep trying it and keep finding that it just isn't overly profitable compared with the more traditional modes such as large buses on a scheduled timetable.
There is one outlier - car/van clubs - but they are just a different car hire model, not a massive paradigm shift.