It's an antifragile plan. They would have to invest little to port and keep Maemo running on these new terminals. But if it takes off it can give great ROI. Also, it buys them independence and differentiation.
They should also provide AOSP for these phones, so that we don't get yet another Android terminal that gets no updates past a few months. It'd be nice to have alternatives for pricy Pixels to run CopperheadOS.