Afaik true rebalancing isn't in the works. Some limited add-device and remove-vdev features are in progress but AIUI they come with additional overhead and aren't as flexible.
btrfs and bcachefs rebalance leave your pool as if you had created it from scratch with the existing data and the new layout.
But credit where credit is due: for a long time, ZFS has been the only fit for purpose filesystem, if you care about the integrity of your data.