According to that post, "You don't have nights OnCall" applies only to SREs covering the systems of the highest profile.

Which is not even all SREs

Anyways SREs are software developers as well.

The distinction SWE/SRE came up to be in times of SOX compliance; nowadays there are also some oncall-related distinctions (that SREs are more likely to be in such multiple-timezone-office teams, for instance, could be true).

You don't have to be on call to have that skill.

BTW, the google model works for them... i'm being more in general since the issue was facebook vs google vs everyone else that I was replying to.

Incident response requires an incident responder. That is, a person who is alerted when things break.

That person (or persons) is defacto on call. If you are never responsible for responding to incidents, your ability to respond to incidents will atrophy.

I would advise such a person works during their normal 8-5 and that "on call" is just a form of work intake for a normal job - not an exception that happens after hours or on weekends when most people refer to "on call".

Ok, but then what do you do on weekends?

Like you still need people, who have the skills to do the oncall work, to man the pager during off-work hours.

Hiring a weekend person doesn't work (they don't have the skills since they're not really part of the team, + bus factor). Forcing people to work weekends doesn't work. Some sort of rotation seems the least worst option.