-
I've seen floors leveled like this (using hardboard instead of ply). By large scale I mean the slope has been over 8ft.
I'm not sure about the scale of the drawing but it might be more difficult to do if it's over a short distance because the pieces of board will be narrow.
Regarding elegant, I mean that it's a time consuming bodge. Elegant would be a clever way of adjusting the existing floor to meet the level of the concrete but I'm pretty sure that is not an option.
Airhead-
It'll be about 3-4m wide and a drop from concrete to floorboards of approx 2 inches at most. Though it's angled so starts at 2 inches one end, down to about an inch at the other.
Can I ask if there's any reason for hardboard over ply? Happy with whatever's most appropriate. I'd have assumed ply is more flexible/can tolerate changes in angle better?
CYOA
For the idiots among us, what do you mean exactly? Not worried about elegant so long as once the vinyl tile is on top it doesn't look like shit. But realistically it will be an improvement on the current situation.