802.11 AMPDUs already tie up the link for ~4ms in normal operation. Without this, the medium acquisition overheads kill throughput. But you're correct that a

802.11 AMPDUs already tie up the link for ~4ms in normal operation. Without this, the medium acquisition overheads kill throughput. But you're correct that a single 64KB packet sent at MCS-0 would take a lot longer than that. 802.11 already includes a fragmentation and reassembly mechanism at the 802.11 level, distinct from any end-to-end IP fragmentation. Unlike IP fragmentation, fragments are retransmitted if lost. So you could use 802.11 fragmentation for large packets sent at slow link speeds to avoid tying up the link for a long time.