I don't know much about LineageOS Malakai, but my guess is the Pro1 being quite unique, chances are good that the LineageOS maintainers will keep supporting it for as long as they can, at least until a better replacement exists, and I don't see any in the near future (the Pro1x is basically the same device with more storage, RAM and a different layout, they'll both run the same rom). Just like how the N900 stayed afloat for years with CSSU and now Leste to replace closed source bits because there was no alternative.