As I've said before, I really think the creation of the second modem instance for SIM2 belongs in the mtk device plugin.   Creating it sets a precedence that that the rildev plugin knows details that really are specific to the device plugin.  I'd even go as far to say the socket paths also belong in the device plugins.

If we keep this paradigm, adding a new rilmodem device plugin would require this plugin to change, whereas if these details are handled by the device plugin, then this plugin remains nice & simple.