The whole premise of running regional Eurostars and through sleepers was flawed, not helped by some very dodgy demand modelling that was done in the first place. As told to me many years after the event: Demand modelling was undertaken to establish where the North of London (NoL) sets and Sleepers should run from, if at all. The original questioning was somewhat loose, such that the "market" was considered to be anybody who had ever shown any inclination to leave Great Britain by any means in any direction. So (for example) if you lived in South Yorkshire and flew to Benidorm once a year, you were counted as a potential Eurostar / night sleeper customer. Likewise there was a very strong demand at Plymouth for journeys to the Continent, so a portion of the sleepers was planned to start from there. Ferries to Santander and Roscoff played a part in the statistics, plus Navy personnel.
There's a strong feeling that it should make sense to run North of London Eurostar services, but London is actually the problem. As a city, it's amongst the biggest in Europe, and has pretty much everything on offer (apart from guaranteed sunny beaches). Passengers on a NoL train have to make the deliberate choice to avoid the obvious easy destination and go somewhere further away which may be more expensive and offer less.
Wearing my cranking hat, I'd love there to be through Eurostars to points north, but I can't see it happening any time soon.