We in the Hebrides had an extensive lot of cable-laying some years ago and iirc the Orkney group of islands were interlinked well. But it seems that, for some reason, the Shetland group’s islands were forgotten back then. Now, it seems, Shetland is being linked to Orkney via the island of Sanday which is one of the furthest northernmost Orkney islands. Presumably that link connects there to the existing link from Sanday to Orkney ‘Mainland’ (which is the largest island in the Orkney group and not to be confused with the mainland of Scotland).
(Having your map open will help.)
Burakkucat mentioned the shore where I am, in the village of Heasta on the west coast/atlantic coast of Skye. A fibre cable running from the village of Ealaghoil down the atlantic coast of Skye to Tarskavaig south of us, or even down to Mallaig on the Mainland, calling in at many small villages such as Heasta would provide valuable redundancy for us if we also had a direct, short link from Heasta to the village of Broadford, which is about 4.5 miles north of us. A coastal link would not make sense as a way of serving Heasta alone, given the fact that there’s no convenient existing connectivity elsewhere along such a coastal route, and also given the fact that Heasta is so near to Broadford overland, where plentiful existing connectivity can be had. But if a link to Heasta could be a stepping-off point to all the rest of the west coast villages of South Skye then a Skye west coast run would start to make sense. Indeed, serving Tarskavaig only via Heasta and the coast could make sense, saving a long overland link.
I’ve no idea how much short ‘hop’ undersea links along a coastline from place to place cost. The hop lengths would be modest, and there’s mains available at every stop-off landing point.