Now that adaptivity is fully implemented bucket mode is obsolete and was removed.
seems that adaptivity in 1.4 is useless ! (strange render time)
just denoiser with noise limit is good feature!
Well it has sped up every single Scene I rendered for the past months. Same for other people. It only has a small recalc penalty every 5 passes, but in return you get not having to sample noisy parts of the image for more time than other parts. Adaptivity for me has made the single most biggest difference, for many others who test out the daily builds aswell.
If you think you found a place where adaptivity does not improve sampling or even makes it worse, report it as a bug with how to reproduce or a example scene, devs will jump on it and fix it in no time. But so far not a single complaint has been posted with actual evidence, thus adaptivity runs just fine and as it should. It is a silent image improver, not as flashy as increasing rays/s or denoising.
Your feature reqeust concerns Memory management. This has not been changed at all. If you have memory issues there are ways to help that instead.