only to bring it back temporarily with batteries that don't qualify for the full federal tax credit, then take the line down again later this year to implement Highland updates
That's a good point, it does seem strange they'd introduce a new battery pack and not do it at the same time as Highland. So, maybe they are doing it at the same time and Highland is ready in a few months? Or swapping out battery packs has minimal disruption to the production line. That might be the case if externally this new pack is the same and it's just coming from another supplier. Tesla has proven to be quite adept of being able to use a variety of cells and cell form factors in their cars all at once (Model Y comes in 4680, 2170 cells from multiple manufacturers and I think an LFP variety from Shanghai).