The thing is, HDR is considered too expensive and impossible on these cards without specific hardware capabilities and relevant API support.
Valve said "Ha, let's see!" and implemented great HDR visuals with integers only. So it's not just let's hack together and see how it goes. IIRC, it took three re-implementations to get it right and performant.
Similarly, I'm not a stranger when it comes to hardware and its limits, but what deemed impossible by many, even knowledgeable people, doesn't mean it's a hard, cold truth (e.g. demoscene and PoC||GTFO).
Valve said "Ha, let's see!" and implemented great HDR visuals with integers only. So it's not just let's hack together and see how it goes. IIRC, it took three re-implementations to get it right and performant.
Similarly, I'm not a stranger when it comes to hardware and its limits, but what deemed impossible by many, even knowledgeable people, doesn't mean it's a hard, cold truth (e.g. demoscene and PoC||GTFO).