It takes as long as it takes to debug the issue and create a fix. Plus it’s a non-critical issue so wont get the same attention as a site-breaking bug would for example.
For years production experts, and experienced streamers, have been saying don’t use VBR unless you are aware of and accept the downsides to that choice. Yes CBR will use more bandwidth but adjust it accordingly so it’s appropriate for whatever bandwidth limitations you may face. As for disk space and recording, depending on what setup you’re using it could be possible to record at a different bitrate to that of the stream feed.
If you feel that Twitch are going backwards, you can report 3rd party dev issues here: Issues · twitchdev/issues · GitHub
First party issues here: Twitch Help Portal
And if you have suggestions on how Twitch can improve them make the here: https://twitch.uservoice.com/
Voice your opinion where it matters, threatening to move to a different service on the 3rd party developer forums does nothing to improve the situation, you are free to use any service you wish.