If there is a reason to want to in-house the fabrication of chips then it seems silly to not extend that to at least the boards that house them, otherwise we wind up still being reliant on an international supply chain which seems to defeat the purpose.

Even if it was just motherboards in particular and not others, that seems like a necessary step in securing the supply chain and if we only do that for national defense the benefits of competition likely won't extend to consumers that are still exposed to trade taxation.