I think that the fixed fee 'per passenger' for travelling through the Channel Tunnel, plus the share of Security and UKBA costs (these don't come for free!) would not be covered by £30ish tickets. Perhaps there are hidden costs which cause Eurostar tickets to be not cheap, which even 'Izy' service would not make much of a dent in?
Eurostar charge £16 to make a booking with loyalty points as a so called 'network fee' (introduced in a few weeks). This implies the variable costs to them of those non-negotiable 'per passenger processed' fees come to about that amount, which would leave £14 left over for all other costs and any profits. Eurostar also used to sell a small number of cheap fixed tickets at £29 although only when booked as part of a return (all Eurostar tickets are now free to amend, at least before 14 days to departure)
So it doesn't seem that £30 singles as a starting offer would necessarily be too cheap, although clearly what we don't know to what extent the £260 Business fares on Eurostar go in cross subsidy of their cheapest standard rates.
A starting price of £35 would still undercut Eurostar and compete with airlines, although I accept that that may still be too thin to cover all operating costs and make a profit, even on a full 1000 seat train. Like Izy, Ouigo and others it wouldn't stay at £35 as the train starts to fill, it would go up to £45 and £55. Those rates would still be competitive against Eurostar at any time but their quietest.
Of course there'd need to be enormous capital to start such an operation up, although far less than for a Sleeper service, and I don't think that will be happening any time soon.
To put it another way, what the environmentally conscious traveller really wants is for the railways to put careful downwards pressure on costs, which is entirely the opposite of what Sleepers do.
