KKrieger is a tech demo, it's not even remotely practicle for using in a game. It's extremely slow rendering, even with levels and models that have minimal detail.
I think Qfusion pretty much has everthing you are looking for, and would still be scalable for lower end systems. From what I understand IOQ3 is never going to be adding any hi end rendering fx, so you're gonna be stuck in 1999 visually with that engine.
first of all ioq3 is strongly considering upgrading their graphics, and second of all qfusion doesn't look that different between my radeon 9250 and radeonhd 4670 (only differences are world outlines, bloom (which is ugly), and shadows, all 3 can be done without the fancy hardware)
What about bumpmapping, specular mapping, parallax and offsetmapping, distortions, etc?

We didn't use them much at the last version cause we are still upgrading the media, but they are used at some maps. Of course QFusion will never look like XReal or those other engines. It could be said that XReal is to Doom3 what QFusion is to Source. Of course Source isn't the paradigm of rendering features, but when it comes down to making games it's a very practical choice.
I agree that the bloom is crappy. It was cool by then, but it sux compared to HDR which is the common filter now. I'm trying to convince Vic to implement it, but didn't get him convinced by now. :/
Anyway, if ioq3 implements the same thing (cause I asume they'd go with deluxemapping, not real time) plugging warsow's renderer into Trem isn't worth the work.