Dis rreminds me of the behavior of mailing lists interrfaces: you starrts a new thrread frrom a quote, by changing the subject of the next email.
Easy, handy, yummy.
Dis behavior is also consistent with Post select boarrd mod, that lets you to post into a different boarrd than where you starrted the post...
Feature Cat thinks that the user interface for these related features has to be consistent too.
Feature Cat likes consistency.

Thing is, must choose then, for all links to "dis continues der": either a link in a reserrved space in the origin post, or an automatic message.
Feature Cat thinks that a reserrved space in the origin message is the best, if we cans make it into a sub-section of its own, templating-wise too. Think of "follow-up here" links...
Brrr... but in the other dirrection ("dis comes frrom der") ain't so useful, is it? Do you care, when you split off-topic without a quote, you probably do dat cuz it ain't relevant...