Good to hear of new sail rail tickets appearing (rather than gradually being cut back which is what usually feels is the trend).
However there are a lot of details to be addressed to make these journeys easier for people to book and carry out, if they are going to be tempted away from flying.
I did Dublin-Holyhead-London a week or so ago using Irish Ferries.
It's not easy to work out how to get to the port from dublin city centre. The Irish ferries website suggests you can use a regular dublin bus service (but provides dead links to the information) and then recommends you use an "express shuttle" run by Nolan's Coaches which is what I attempted to do. You have to navigate your way through some slightly confusing PDF timetables (different on different dates) and work out where the bus stop is (which is not at the bus station or either of the main reason stations).
On the day I tried this the bus simply didn't show up. Two other people were waiting too - we'd all independently come to the conclusion that this was the right place, and a sign at the bus stop confirmed it. Eventually we had to get a taxi at the last minute and just made the ferry. Because we could split the cost it wasn't too bad but if I'd had to pay the taxi fare myself it would have been going on for half the cost of the whole rail-sail ticket to London.
What was worst about this experience was Irish Ferries complete disinterest when I complained (by email) after the event. All they would say was they don't operate the bus so not their problem. I tried to say that maybe they had some responsibility to check that the info on their website is reliable, and that they would have a bit more leverage than I would in following it up with the coach company. But, no interest, computer says no. It certainly left me with the impression that they are not really bothered about the experience of rail-sail passengers.