HEX will remain on the market mainly for business travellers, as companies are paying - they don't care about the price. It is £5 extra on board but surprisingly people were and still are buying tickets on board because... they don't care about the price (once again - they expense it). Obviously since introduction of gates it is less passengers doing that but... There is still many doing it on purpose so for example - they use free ITT ticket at Heathrow to go through the gate just to catch the train and they pay Standard fare on board.
Although they started being "family friendly" with kids travel free and with Group Saver offer to encourage families and friends travelling together to use their service, they always were and always will be premium service for business travellers. As someone mentioned before, in fact they'll be able to work more during 15 mins journey on HEX than on 30 mins journey on Elizabeth if it will be packed with commuters to intermediate stations. And they definetely prefer non-stop service instead of stopping service - well who doesn't?
Upgrade to First Class is and will be possible with on board staff who will remain to work on the train and check tickets (for purpose of first class revenue protection as well as people with wrong tickets or using discounted tickets - and this is because gateline staff on each end is not Heathrow Express employees so they do not collect revenue from customers even if they come without correct ticket).
Trains are "DOO ready" but they do not run like that. There is always trained member of staff on board for safety reasons.
The gate line is now complete, and the launch date is
mid-November.
Gateline is ready since earlier this week and it is meant to start tomorrow. Although Oyster cards meant to start operate on HEX at the same time, they might be delayed. We'll find out by tomorrow.
About the Oyster fares - remember that HEX is offering Advance tickets to buy online, Return tickets with discount, Railcard discounts, airport/airline staff discounts and Group offer - and none of these will be available on Oyster cards (obviously apart a few Railcards which you are able to load into Oyster card, but again - it won't work on Return tickets).