On that subject, I saw a write-up about antigen tests earlier today that also covers Omicron duration:
https://yourlocalepidemiologist.substack.com/p/antigen-tests-real-world-data
References a few studies covering Omicron duration, indicating a range of times for clearing it across individuals, with one study showing "Roughly 50% of people still had a high viral levels at Day 5 (meaning they were likely infectious)", and UK data indicating "During a 5-day isolation period (and not using an antigen test), there is a 1 in 3 (31%) chance you’re still infectious." (although note that particular UK modelling study referenced was based on Delta data, not Omicron).
But it's pretty clear a significant number of people will still be infectious after five days. When the UK recently switched to being able to end isolation on day 6 with 2 consecutive negative rapid lateral flow results, the Department of Health and Social Care
officially stated that "If you leave isolation on day 6, after 5 full days of isolation, between 20% and 30% of people are still infectious. The percentage of those released while infectious is reduced to around 7% if people have 2 consecutive negative tests and then leave isolation from day 6."
Even 7% is quite a lot of people. So yes, a lot of infectious people will be exiting isolation, even with negative tests, let alone positive ones.
I'd view that as too many, resulting in further preventable infections and an unnecessary increase in risk for vulnerable and immunosuppressed people, particularly given that presumably some of those people exiting isolation early while still infectious will be returning to healthcare settings.
But I suspect the calculation isn't about the individual risk, or the risk to those groups, but whether the perceived economic benefit from allowing people to leave isolation earlier outweighs the potential economic hit from additional further infections. And a crude estimate would indicate that while more people will end up isolating (due to more infections), they'll be isolating for less time each, resulting in collectively less time lost to isolation unless there was a very high number of further infections. And in specific areas, like healthcare, which are struggling due to very high numbers isolating, the same sort of calculation would suggest more staff availability overall despite further preventable infections.
So I suspect that's the trade-off being considered, and I'm guessing they view the increased risk to individuals as acceptable given vaccination availability. I'm not so sure, to put it mildly.