I don't foresee them adding any more HD broadcasts in our area, because there's nothing left for them to simulcast off their AM properties.
As I remember it, at one time Cumulus had HD on WBLX, WYOK and WJLQ. My guess is those three encoders are what we're hearing now. The one on WYOK was turned back on for WDLT, and is simulcasting the Mobile AMs WXQW and WGOK. One was moved to WXBM for the WCOA simulcast, and one was sent to Fort Walton for WZNS to simulcast WFTW.
Unless there's something I'm missing somewhere, I don't think it'd be worth the expense of setting up HD on another station at this point. Without translators they really have no reason to run secondary channels, too.