D is a dead ringer to Xi Yazhou's "elongated flying wing with stubby wings and vertical stabilizer" theory.
I understand there's some enthusiasm about speculating what kind of configuration H-20 may be -- but we're in 2021 now and the configuration of H-20 is as good as confirmed.
Unless something new comes up from someone credible, there's really no reason to keep bringing up alternative configuration as if it is still a reasonable question to ask.
As for that particular image is obviously just illustrations of various generic bomber configurations that were shown as part of whatever paper it was in:
a - subsonic, non-stealthy, configuration reminiscent of B-52 or other subsonic bombers of the era
b - supersonic, non stealthy, seems to be variable geometry taking after B-1/Tu-160
c - subsonic, stealthy flying wing, obviously takes after B-2
d - supersonic, stealthy, just a notional configuration
Obviously none of them are depicted to scale with each other either.
If you're going to depict or develop a higher speed, stealthy bomber aircraft, chances are it will be some sort of elongated delta wing aircraft with or without some sort of slight cranked wing, with or without some kind of small tails.
I wouldn't read too much into it.
If the PLA is pursuing a higher speed stealth bomber to complement H-20, we will hear about it in time.
