Contrary to what you have been thinking, apparently CX is considering to make the 777-300ER a dedicated regional fleet once the A350 and 777-9X arrives and takeover some long haul routes. This is word from a CX pilot. CX are still doing the calculations on whether doing so will be cheaper than investing in an entirely new fleet of regional aircraft. After all these are plans that will only solidify in about 8-10 years time, by then the 77W might be considered "old".

I find it interesting that CX is trying to go down to this route, since 77W is a very premium plane as you said, especially the 77H. If CX wanted to make this plan work they would need to seriously reconfigure those planes to suit the regional market demand.

But of course I don't have the numbers of how the operating economics of A350 and 777-9X compares with the 77W, so can't be too sure on what CX is thinking.