Hi Bubble, just felt the other thread wasn't a great place to chat about this one.
DS found it very easy to settle into Interhigh - it's very much "school" with a group of children in your class, subject teachers, homework, timetable, etc. The only differences really are the technical part - DS was quite comfortable using a PC so that didn't give him any trouble. Plus the fact that you are only getting the academic subjects so you still have time (and need!) to do other things to cover stuff like art, music, PE etc.
And while some social skills are the same over the internet - dealing with different personalities, working as a group, etc - you still need the face to face interaction of RL too, so you'll want to look at what groups etc he gets a chance at.
DS was in school till S2 (Yr9) and didn't have any issues with the whole school way of doing education, so settling in was fine for him and I think should be ok for your DS too. The problem would be more for someone who had got used to autonomous education and wanted something more structured eg for exams - they'd probably find the lack of freedom strange at first.
HTH