As to the other thread you mentioned, I'm fairly certain there are no updates there. Marketo can only see campaign Member status, not identify the hierarchy between parent-child.
Also, technically in SFDC, a member of a child campaign is not automatically a member of the parent campaign. They are counted in the total hierarchy, but they are not members of the actual parent campaign (meaning triggers on the parent campaign would likely not fire anyway)
With a separate Marketo Flow or an SFDC workflow rule, you could add leads to the parent campaign as soon as they are added to any of the child ones, which could then make the parent campaign trigger work. But doing this might mess up your reporting if you do ROI or Lead totals with Campaigns.