It's something that they have already mooted up in Orkney where they are using the stored hydrogen while the internal North Isles ferries are in dock.
The problem at the moment is that the internal fleet is at the end of it's life, and there is no real consensus what the future will be - more fixed road links or new boats. New boats could mean hydrogen-powered, but the Council doesn't have the money to properly fund any of the available options. The internal ferry operator in Orkney is a private operator wholly owned by Orkney Islands Council, and current thinking at OIC is to offload Orkney Ferries to the Scottish Government, or in other words nationalise it.
The Western Isles already have a similar arrangement, the main operator CalMac is owned by the Scottish Government, and several new boats have been funded recently.
Whilst national usage of wind power varies a great deal, there are areas like Orkney which have a much more reliable supply of wind power, and Orkney is self sufficient in electricity generation for the vast majority of the time. Indeed, Orkney usually has a surplus and exports electricity, but further development of wind generation is being curtailed by the size of the cable between Orkney and Scotland.