I would suggest that CWL-CDG is not a low cost route. Low cost routes need serious volumes to make them viable, that is the basis of the business model.
There is some leisure traffic on the route, at leisure fares, but to make it work as a business route it needs to be at least double daily. Which means that, if you put a standard low cost airline aircraft on it, you are looking at producing roughly 640 seats a day, and a low cost will want to fill nigh on 500 of them, day in, day out. Way too much for CWL-CDG, as baby proved. You'll notice as well that easy don't run CDG from BRS, for similar reasons I would bet. So you need a smaller aircraft - which takes out the serious low cost players.
Jet2? Don't think so on this run - would be an orphan route for them, since I really can't see them basing a 737 in Cardiff any time soon. And in any case, the 737 is too large for this route.
ASW? Pride themselves on low fares, and will fall foul of the CDG route economics.
Aer Arann? Interesting thought, but they have shown no interest in Paris from anywhere else (although only Luton makes any sense for them), and in any case, they are short of aircraft and crew at the minute. Probably wouldn't want to take a flyer on a route like CWL-CDG. And anyway, they'd want PSO
Flybe is interesting. But again, they would have an orphan route here - would they stop at EXT on the way over the top?
BACON is the logical one, but this would be their only route out of Cardiff. Makes no real sense unless it was operated on a W pattern, and do they have a spare aircraft at the right times of day? I somehow doubt it, morning and evening are BACON peaks, since business travel is their niche (despite their lunatic low cost strategy).
My money remains on Eastern....
Eastern to CDG would ,as said, be very expensive this would not appeal to the general public!
to which I say, the "general public" are not your target market on this route, business people are. Airlines are there to make money, which BA did with their relatively healthy fares. Even when the good people of South Wales were offered a low cost flight to CDG with Baby, they didn't exactly flock to it. The equally good people of the South West don't want to flock there either, clearly, or otherwise easy would have gone toe to toe with BA from BRS by now.