You won't see a firmware upgrade with memory adjustments, no -- and no, an Alienware system is not essentially the same as the XPS -- it's a completely different system with completely different design parameters.  
The new XPS comes with DDR5 4800 Mhz. Cru cial has released new DDR5 SODIMM with 5200 Mhz and 5600 Mhz. Previously, the recommended upgrade for the Dell XPS 9720 was the Cru cial 4800 Mhz ram. (Non dell route of course) With the 5200 and the 5600 now released, will these speeds work with the Dell XPS 9720?
Cru cial Released new DDR5 speeds up to 5600Mhz