I've linked this video before but there is something significant at 2:25 an image shared at Battery Day..
We could call a Structural Pack a - "Cell Structured Pack".
And a traditional 2170 pack a - "Frame Structured Pack".
The difference being in the "Frame Structured Pack" the cells are cargo, just along for the ride. The frame provides the structure.
The Structural Pack is, lighter, stiffer and has the weight more centred, but we know a Model Y with a "Frame Structured Pack". is viable.
Like Jordan, I know think a Structural Pack and a "Frame Structured Pack" are interchangable, at least in a Model Y with front and rear castings.
So if necessary, I think regular 2170 packs could be used for the initial Berlin Model Y ramp, and CATL LFP packs could be used in SR+ Model 3 to free up some cells.
For the 4680 ramp there may be an internal target, and an external target, There may be deliveries of Model Ys with those cells to Tesla staff 3-4 months before customer deliveries... If Tesla wanted to do that, it probably would not be overly difficult to accommodate.