When will it be there?
You mean blending on a float buffer? Well, maybe next HW generation.
I think that float-rendering is not truly useful without FB-blending.
Think of adding the contributions of multiple lightsources that cast shadows, like in Doom3. You could emulate that with a ping-pong render to texture, but what about …
… a true HDR particle system. Like RTT for each particle? Oops
No doubt it’s useful. But then again, you can’t have everything you want. Chip space it limited, so sometimes you have to settle for something not quite as good.