Since we're indulging in speculation, here is mine.
Lionel licenses TMCC for Atlas O products but has reserved the more advanced Legacy system for its own products. Atlas O hasn't used Legacy either because Lionel would not license it to them to preserve its exclusivity or Lionel required a higher license fee than Atlas was willing to pay. So, Atlas has had to use an inferior system.
It seems that MTH will be continuing to make, upgrade and license DCS, which also includes DCC that can be used for 2-rail O scale, a market segment to which Atlas sells. Therefore, by using DCS under license from MTH, Atlas O will have a system that is competitive with Legacy. That's why I expect to see Atlas O products exclusively with DCS.
Just conjecture on my part.