I haven't read that article, but I strongly believe Heathrow Express will keep going for a good long time yet. If I'm in London and I want to go to Heathrow, I aim for the Heathrow Express. Yes it is expensive, but I like it and I'd hate to arrive at Heathrow from central London on a 345. That would be preferable to a ride on the Piccadilly line, granted, but I'm certain I'm not the only one who likes to travel to Heathrow in some sort of actual style.
The holiday experience begins once I board the Express as far as I'm concerned, and ends after I get off it. I'd not feel the same doing the journey on a 345, and I tested this theory some time back with a 345 on a day when they were using the main lines. It's absolutely not the same, I didn't enjoy the experience at all. It was nice to be on the Down Main, that much is for sure, but doing Paddington to Heathrow on a 345 just didn't feel right.
Heathrow Express is certainly the more premium option, no question of that, but is that a bad thing? Not all of us want to cram into a Metro train at Heathrow, or on the way to Heathrow! Yes I have to pay a lot of money for the experience, especially as I don't tend to book it in advance. Last time I did it, it was very much an impulse purchase to clear the Express 387s for haulage, £37 for the privilege but money very well spent when I got to avoid the crowds on the way back!
I like CrossRail, it has transformed travel across London, but I would not want to do a 345 to Heathrow with luggage!