I'm not sure I understand why you think it a good idea to restrict writers from posting once they finish their story for several weeks.

The uncertainty of updates in case of WIPs is a risk anyone can decide to take or not. There are some very long stories and some people who can't work constantly on their stories due to RL concerns - I would not wish to lose their stories because a rule would prohibit them from beginning to post until the stories are almost complete. Also, some writers use reader feedback to modify the story as they go on writing. Reader feedback can also encourage and motivate writers to go on and continue writing, while the motivation might wane if one is writing a long story for only their desk drawers (hard disc drives) without encouragement.

I'm sure the readers can bear the 3-day rule for the sake of all writers having their time on the board, in the very rare cases that the writer is all ready to post again but can't yet (or the writer can post a longer segment). The waiting is the worst when it's long and uncertain.
Just some thoughts in favor of the current rules.