CabinCrewe - the only airlines I can think of (and I admit I'm struggling with credibility here), are Ryanair doing a STN-GLA run (rather than PIK), Flybe doing something from LGW or a Lufthansa group carrier taking some of the connection market by opening a route to FRA
The point I'm trying to make, is that if it's become worthwhile to put a widebody on a route where frequency is important, then there's probably rather more demand for transport than is currently being supplied. The train in comparison just isn't fast enough to be a credible competitor. When a market becomes too juicy, economics says that someone else licks their lips and says "I'll have some of that"