Make oxygen a chargeable extra (oxygen as a service)

The quiet rollout of the new trial on board the 08:19 (Monday 23/04/2018 carriage No. 1 Surbiton->Waterloo) seems to have been a pretty good success so far!  

My observation, feedback and comments for future improvements:

• Cheaper to run.  By not having any air conditioning or air flow whatsoever you must have saved a sack load of money - great!
• Scales well.  You can just turn off all the air conditioning units to simply scale up the cost savings in an instant.
• Sedated money units.  Since they will quickly become drowsy and sedated in a matter of moments they will be much less likely to lash out, kick or stampede.  Of course they won't know prior to loading as you don't tell them, so they won't know to avoid the carriages.
• Next stage - Make it chargeable.  You've already saved a vast sum by implementing the above, great!   Here's the opportunity - those units who might want to either read, listen to music or to otherwise not fall into an oxygen-starved brainless heap on the floor, you can provide small oxygen canisters via a dispenser on platforms.  My initial research recommends a £5 charge per journey.  Make sure the canister only lasts for the duration of the trip though - you don't want to encourage unnecessary brain function.  The new service would require them to scan their ticket at the dispenser so it is programmed to automatically stop the oxygen supply a few minutes before arrival, so they arrive somewhat sedated, ready for work.
• The final benefit is that you are not  bound by annoying ticket price increase limits every year.  The sky really is the limit on the price of the oxygen canisters! 
• One negative point though.  Alas, so far I've not been able to purchase an oxygen canister as they were not available, which was a bit disappointing.