Congratulations Trent, this looks really cool.
This new design does seem to address some of the slide width and side profile complications around the original ATOM adapter design and should make it more flexible in that regard. It also appears to be a simpler machining problem to solve. Well for us that don't have 4+ axis CNC machines anyway.
WRT to HK slides it might provide something depending on whether the 'key' feature milled into the slide doesn't interfere with, or can made to accommodate the firing pin block and roll pin holes that make the HK slides more difficult to install optics on.
Trent is a really clever guy so if there is a way I'm sure he will figure it out.
The integral rear sight
as shown seems to be limited to a plain black sight since the fore/aft dimension looks too thin to take a Tritium vial. Of course that may well be in the works.
The same problems remain WRT optics that have different 'deck heights' since the rear sight height needs to vary to maintain a consistent engagement in the optic window (or even be visible in the case of the DP Pro). So front sight would need to be varied to accommodate the taller/shorter integral rear sight.
Also, the height relationships between rear and front sights vary wildly across slide models, calibers, etc. All variables that get taken into account in installing an optic on a slide.
Like any integral rear sight solution (e.g. Trijicon 1911 RMR adapter) on slides with out a windage adjustable (dovetail) front sight may not have much in the way of windage zero control. This is primarily Glock, CZ and Walther.
This presumes that a precise zero of the irons is even required.
These take nothing away from Trent's design and are just things that need to be solved for backup sights on optics equipped pistols.