*Really? I wouldn't (feel the same that is). Presuming it's important surgery, not a jolly id do anything to get seen sooner. Key to the idea is they would obviously tell the reserve people that they were reserve and it would be voluntary, so they wouldn't be expecting surgery and then going home disappointed but would know from the start they might not get seen - and if they didn't their next date would be definite.
You would need to have 1 day off work anyway, and if it was like ops example the surgery team would know early on whether the original appointees had turned up or not so the reserve people wouldn't be hanging around for hours not knowing.
I dont think you can make overall judgements about "people who work" anymore. So many people are semi-retired or work remotely and flexibly now - for me the inconvenience of making myself available for a few hours would be very minimal given the potential benefit so I wouldn't think twice about volunteering.
Obviously it wouldn't work for everyone or be completely fair for those who can't easily amend their working hours, dont live nearby, sort childcare or take time off, but no systems are equally fair for everyone - even if only a few people could be in the position to jump in last minute or wait around as a reserve that still makes the overall waiting times shorter for everyone and is better than appointments being completely wasted?*
Yes really, because that is not an insignificant list of circumstances that taking a day off 'just in case' you get seen doesn't work
Of course taking a day off for surgery isn't an issue (plus planning recovery time etc), taking a day off/rearranging everything and then finding out you aren't actually getting this long awaited surgery and will need to reorganise everything yet again pissing off work/calling in more favours for childcare and transport is not.
As you say it would only work if people volunteered to be 'on standby' and they gave people the chance to opt out of it
Personally my experience of the NHS is that they couldn't organise a piss up in a brewery so I wouldn't hold out hope either way