Also the allowable variance between UTC and ut1 is 0.9.
Five minutes - no problem at all.
If the offset rose to 60 minutes, I know people complain bitterly twice a year when we change the clocks by an hour and they lose an hour of light for sports in the evening, or lose an hour of sleep. But with leapseconds taking ~0.5 seconds a year, that won't be a problem for a few thousand years.
[1]: Because allowing the time to drift microscopically from human perception is indistinguishable from not changing it, only that after a sufficiently long time you live in a time zone shifted by a constant, only there was never really a big event to shift it. It’s like getting old - you don’t notice it, until it’s already happened.
The OP proposal does say UTC should be used when representing time to end users, but in practice there is going to be blurry lines.
¹TBH, still confusing enough to introduce quite a bit of friction when comparing graphs etc for outages.
I feel like we should be able to easily "bundle" leap seconds into existing leap days on leap years. Make February 29th just some random number of seconds shorter or longer than, say, February 28th. Most people feel February 29ths are weird anyway, few people would probably notice when they have strange amounts of seconds in their final hour. Some software might hate it if Feb 29 23:59:56 rolls over to Mar 1 00:00:00 or much more rarely there's a Feb 29 23:59:62 (or using the existing Unix time "smearing" technique, some Feb 29 you get three or more Feb 29 23:59:59 timestamps in a row), but other than that it would 1) be on a predictable day, and 2) a day that's already a weird every 4 years except every 400 outlier that's already expected to be an edge case.
Intuitively it should be synchronized, but giving it more thought it is not entirely obvious why; e.g. my current local time zone is more than half an hour off of local solar time, and that isn't really a practical problem, so if UTC would be, say, five minutes off of actual solar time in Greenwich, what issues does it cause for people? Astronomy would be using specific time systems and/or adjustments anyway.