Out of curiosity, I wonder how many people in the West Country will actually consider flying from CWL? Maybe people north of Bristol near the M4/M5 corridors? But for myself, I just won't consider it. Not out of spite, but it's just too much hassle to get to, and I can be at Heathrow just as quick and have more options there, so for me it will pretty much always boil down to BRS or Heathrow (or Gatwick if I'm really desperate)
In terms of overall passenger numbers the last published CAA survey for BRS and CWL was for 2012. That showed that 30,000 passengers (or to be more precise passenger journeys) of CWL's 1.013 million total that year were made by travellers having an origin or final destination in the South West, which means the entire South West Government region, ie Gloucestershire, Wiltshire, Bristol, Dorset, Somerset, Devon, Cornwall/ Scilly Isles.
As a comparison, 1.098 million passenger journeys of BRS's 6.125 million total in 2012 were made by travellers having origin or final destination in Wales.
I am in no doubt that the CWL Qatar route will be used by people living in the South West, especially those in the wider Bristol area. When Zoom operated from CWL to Canada it picked up quite a lot of West Country-based travellers.
It might be that fewer West Country people will use the CWL Qatar route than would have been the case with Wales-based people using BRS had Qatar pitched up there. The main reason for this is that Bristol is nearer LHR than is Cardiff (and there is also a direct motorway link with BHX) and LHR is the default long-haul scheduled airline airport for most West Country-based travellers.
Qatar will need to advertise extensively in the West Country to get their message across. I've never seen much publicity here for their BHX route, nor for EK at BHX for that matter.
I have a personal interest in this. My wife and I fly to Australia via the ME every year to visit family. Because of a medical condition my wife could not fly all that way in economy so we bite the bullet and pay for premium. The first time we went (in 2010) we used Emirates from BHX - business BHX-DXB/DXB-BHX (only two-class aircraft) and first, DXB-MEL-DXB. Although we had obtained a deal from our travel agent, in subsequent years we discovered that for not much more we could fly all the way from the UK and back in first with EK, if we were flexible with dates (via deals this travel agent had arranged). We've since flown five more times to and from MEL with EK, all in first and all from LGW where the deals were to be had.
Because Emirates provides chauffeured cars for business and first travellers (a small top-up fee is charged to LGW from Bristol) getting to Sussex is not really a hassle. We have become sick to the back teeth with DXB though. It's a hell hole and we are actively looking to another airline for our next visit to Oz. Even travelling first you have to make your own way from one part of the terminal, partly by train, to the other through what resembles a football crowd coming out of Wembley in terms of mass.
We had tentatively arranged Etihad via Abu Dhabi in first from LHR for our next visit but personal circumstances mean we've had to postpone that. We've looked at Qatar at BHX more than once but timings from there meant a very long wait at Doha at least in one direction. It would be business class with Qatar, at least from BHX to/from Doha and will be the case from CWL too, but Qatar seems to have an excellent reputation with this product. We shall be looking seriously at what CWL has to offer when details are announced.
The only downside with Qatar is that they don't provide complimentary chauffeured cars for their premium customers, unlike Emirates and Etihad, although with the way Emirates is beginning to cut back on some things I wonder how much longer this service will remain.