Working on both options. 1. Install openthread ncp on the Argon, interesting if it can be done but probably very limiting. 2. Connect regular Argons to a border router for interconnectivity. That is probably the best route. Then the border router could provide an internet connection or the particle cloud could be your internet.
A 3rd route is that Particle actually embraces and promotes their awesome hardware as having openthread connectivity, not easy to work with, like the Particle cloud is, but a free option for the advanced developer or cheap educator. 