As per https://github.com/csrhodes/sbcl/tree/subclassable-structures-rebase
That link is dead.
This is not actionable. I can assure you that the way to get attention is not merely to reopen.
there was no such intention on my side. i just thought that the only reason for the status change was the broken link, hence i reverted that, too.
Bug watches keep track of this bug in other bug trackers.
That link is dead.