I think that's absolutely the key, honestly and it's why I'm a fan of AP/accelerated courses where at all possible. I also think ability grouping is great as you can work with students of lower ability without having to worry about those with higher ability being bored. I think that you need contact with those who aren't self-motivated, even if that's live classes they have to attend, as then they know there's accountability. But I do think that a good self-motivated learner,
who knows how to learn would greatly benefit from just reading texts/watching quality videos (while taking notes) and having a teacher to basically ask questions to when needed.
Sadly, I'm not sure how much of the grouping I'd like to see is legal. I know my school got in trouble for offering 'Core' classes which were basically remedial education classes in core content areas (So you'd have 'accelerated algebra 2', 'algebra 2' and 'core algebra 2'), which worked as you could find ways to focus on real-life examples for those students, but gave rise to a host of other issues. But, overall, I see the only real way to do online learning entirely is through group segregation, at least at the secondary level. Hearing some of our AP teachers complain, it'd almost need to be a double split -- one on ability and one on motivation.
Of course, a lot of the latter, in my opinion, stems from the culture of the area. Sadly I'm in a rural area where well-paying jobs used to be plentiful right out of high school (or even without a degree!) and so a very anti-intellectual culture developed. Sadly, even though those jobs aren't present, the culture stays as most who have other values move out and leave. Me and a few of my colleagues (all from the area) are exceptions, but I know several of us would leave if we could. So you're also fighting a cultural battle on top of all the other stuff.