Cost isn't really an issue for the HEx clientele, they're either rich tourists or business travellers on expenses.
As it stands the HEx is better than the Connect because if the frequency and speed
Then with all due respect (i.e. very little) those people aren't living in the real world. ***dons tin hat***
Speaking as someone who is neither a rich tourist nor a business traveller on expenses, yet has somehow set foot on a Heathrow Express service from time to time, I can assure you there are plenty of people using it who do not fit into either category.
I have never made a habit of it, but there are certain times of the day when using the Railair coach from Reading is a total lottery as a result of the amount of traffic on the M4, or the less frequent Heathrow Connect/TfL services are full of West London commuters. Then it becomes a case of biting the financial bullet on HEx in order to be sure of reaching Heathrow in time for a long-haul flight, where missing it would be a lot more financially painful than either the HEx fare, or having to pay for another flight to my destination.
There are other airports around the world where premium shuttle trains operate alongside others doing the same journey, whether local, regional or long-distance.
The French are going to provide an express link between Paris and Charles de Gaulle airport by 2024 - the commuter-laden RER Line B can often be a less than fantastic 'welcome to France' experience - and if Frankfurt airport was a bit further out from the city centre, I'm sure the Germans would do the same - 10 minutes riding on some of their old S-Bahn stock was more than enough.
Crossrail may well make a difference to travel habits, thanks to the direct link to the City and Canary Wharf, but does anyone seriously think the Class 345 interior lends itself to handling lots of airport passengers with large, heavy luggage strewn about? Just what you don't need mixing with peak commuters in a hurry to get on and off the train.
We may well live to regret the tunnels under London offering nothing much more than a glorified Tube service. Being able to send a number of limited-stop airport passenger-friendly trains between Abbey Wood and Heathrow, just calling at Canary Wharf, Liverpool Street, Farringdon and Paddington, might have been a good idea.