On the GW website, the solitaire is very much in the Elites slot, and I think some of the White Dwarf photos have shown the Soltaire as an elites choice in the army list.
My only reference point is the old 2nd ed CA army list, which puts the solitaire as an elites choice then also.
Strangely, it seems the Shadowseer has taken a downgrade, going from a HQ choice to an Elite.
I do wonder if we shall be seeing a return of the "Great Harlequin," as the Harlies default HQ choice. Or maybe we'll get a "Master Shadowseer." HQ choice which may also serve as a replacement/alternate model for the solitaire as well.