Mark,
Agree, we need to focus on the problem we are solving.
Just to remind everyone (the issue was first discussed in Macao), if the ONU sends frames across all enabled (granted) lanes in FIFO order, it would be extremely easy for the OLT to recover the frame sequence (by frame start time, same as in downstream) and without any buffering at all. But the problem with this approach was that a combination of frames that gets in each grant will be different from the combination of frames that were reported by the ONU to the OLT, so every grant will be under-utilized, and a significant portion of bandwidth will be wasted (see picture on the left below). So, the proposal at that time was to pack frames in grants as they were reported (see picture on the right). That solves the grant utilization problem, but requires the OLT to buffer multiple bursts to restore frame sequence.
In Whistler, I proposed to revisit the fragmentation option so that we are not constrained by the frame delineation boundaries anymore. In this approach, the ONU will start transmitting the next frame in an earliest available grant. If that grant ends, the rest of the frame will continue in the another currently-active grant, if any. Otherwise, it will wait for the future grant. At most one frame per LLID will remain split between the OLT and ONU, while waiting for a future grant. I do not have full proposal or even a clear picture of how this would work, but Duane's proposal to do it in RS and have a signal line from MPCP to RS may help.
Glen