So the main issue with the premise here is that in most cases HDR output requires HDR input, and GC/Wii titles don't come with any. I guess it may be possible to provide such through texture replacement.
Additionally, and likely more critically, the inputs/outputs of arbitrary shaders would need to account for HDR content. It's complicated to work out which / where shaders can be revised and still provide appropriate/similar outputs. It would require generating something similar to the current ubershaders at a minimum, and it's is likely difficult to avoid HDR processing messing up numerous effects, likely requiring significant additional per-game configuration.
So I don't know. Perhaps as a first step one could work out HDR texture replacement, and down-sample everything fed through anything but the basic rendering shaders. Though that's likely of minimal impact without all the other shader revision, which likely requires more work than anyone will invest.
Side note, it always irks me a bit when people point to the "difference between light and dark" as a feature of HDR. Contrast actually seems fairly unrelated to HDR and we saw greater contrast independently from HDR support. The primary advantage of HDR is the ability to display things like blue skies and other subtle gradients without noticeable color banding. Various shader processes can further exacerbate such banding, which HDR shaders help with.
Additionally, and likely more critically, the inputs/outputs of arbitrary shaders would need to account for HDR content. It's complicated to work out which / where shaders can be revised and still provide appropriate/similar outputs. It would require generating something similar to the current ubershaders at a minimum, and it's is likely difficult to avoid HDR processing messing up numerous effects, likely requiring significant additional per-game configuration.
So I don't know. Perhaps as a first step one could work out HDR texture replacement, and down-sample everything fed through anything but the basic rendering shaders. Though that's likely of minimal impact without all the other shader revision, which likely requires more work than anyone will invest.
Side note, it always irks me a bit when people point to the "difference between light and dark" as a feature of HDR. Contrast actually seems fairly unrelated to HDR and we saw greater contrast independently from HDR support. The primary advantage of HDR is the ability to display things like blue skies and other subtle gradients without noticeable color banding. Various shader processes can further exacerbate such banding, which HDR shaders help with.