The only purpose I can see for it is long stories that do a lot of kink-hopping where containing said kinks in individual chapters isn't optimal/feasible. Even then, with the way readers consume content here, you're leaving a lot of readership on the table. You'd get more eyes and engagement by splitting a chapter with two wildly different kinks into two parts and posting them to appropriate categories, even if said chapters are extremely short.
If it's to be removed, there should be a significant transition period where authors can choose to move their works into appropriate categories themselves. Only after authors have been given at least a month to make the appropriate edits and category changes based upon their knowledge of the work should it be relegated to what will certainly be a deeply flawed process of a third party scattering the chapters.
Frankly, there should be a message sent to anyone who has submissions in the category warning them of the coming change as well, and/or a block should be assigned to the main landing pages announcing big changes. The forum is a poor location to announce significant changes. It has never been particularly active and has become less relevant as time has passed.
While I'm on that subject, if you want any level of actual feedback about changes, things like this thread should be pointed out on the main landing pages as well.