One issue is that unlike autocephalous churches in Byzatine-Rite Orthodoxy where they are (supposedly) equal in independence regardless of whether the primate is a Patriarch, Archbishop, or Metropolitan, Particular Churches sui iuris in the Catholic Church have differing levels of independence depending on whether they are Patriarchal, Major Archiepiscopal, Metropolitan, or Others. My understanding is that the power to put bishops in eparchies belong to a synod which only the Patriarchal and Major Archiepiscopal Churches. In the absence of such a synod, I think the such power belongs to the Dicastery (formerly Congregation) for the Eastern Churches.
Another issue may be the number of faithful. Based on the numbers is saw in GCatholic, the magic number that separates exarchates from an eparchy seem to be 10,000. Several exarchates have been promoted to an eparchy. However, there has been a case where an eparchy was demoted to an exarchate. The Slovak eparchy in Canada was demoted to an Apostolic Exarchate. Yet, that eparchy had more faithful than the one in Phoenix.
Not really sure how the problem of the Ruthenian Church is to be solved. I've seen suggestions of them merging with either the Ukrainians or the Slovaks.