The description says Arcane Mage is a work in progress. Is this still the case?

Also, plans to keep updated in Shadowlands?

Which description, where?

Shadowlands version is in active development; test versions start with 9.0 on the releases tab.

Main description on Curseforge, under What is Hekili, second paragraph, in bold no less.

Go ahead and give Arcane Mage a spin. I'll update Curse.