That was me too! LOL.
I still think it would be useful.
lol so you want a default of 0.7 and a +1.0, you sir are the dev's nightmare :D
So in other words, here is where the art vs science limit is. If it looks good, it's good.
I'll do some thorough testing and see what looks best on a certain scene I guess.
Kinda... my point is we already have standards, lots of those things change slightly over time keeping things at a somewhat base level (1.0) keeps things consistent, which I think you mentioned 'consistency' in your subject heading as a priority.
So for example a 'recommendation' would be use 0.7 level IF your textures are already hitting 255 white AND you want to achieve "this effect"... That's a lot of IFs and ANDs (so, very specific to a users workflow). This also assumes ALL the textures you are using do not conform to any current standard, so some legacy standard. So if you clamp your white values to the 'recommendation' your image should not change much but the output of where its used will benefit from this clamped value (the output could be a real-time engine, some particular look you are going for, some company recommendation as they might have other use cases where the value needs to be clamped).
Like I said, I could rant on a lot about this topic since I've been delving deep into materials and stuff for the last few years and changing defaults like that would be an absolute nightmare to deal with since there's a few factors involved.
1. Current standards work with other software (important!)
2. Users can easily create pipelines that work best for them and their team based on particular values and nodes
3. Legacy standards are easy to interpret and conform to new standards. Since 1.0 = 100%, I dont need to interpret new values with a 30% offset JUST for Corona. This also relates to point 1.
4. My point about IFs and ANDS earlier - Keep in mind since workflows do change over time that also means that lots of artists are in the progress of updating or creating new content that already coheres to the PBR standard (turbosquid/cgtrader/evermotion etc), so if they produce a texture at 30/240 values for you and you clamp the values to 0.7 you are actually reducing the final bitmap texture to 30/168, thus you are losing all the values the artist intended your texture to appear as at 1.0 or 100% and it will be 30% darker than it should be. You should always use a value of 1.0 since this always relates to the current main workflow, and if you need to change it then do so knowing that this can bite you in the future as standards are updated.
Point 4 is really driving the point home about why 1.0 is standard, but feel free to discuss why you think otherwise. I'm keen on other peoples opinions since the bubble I live in often needs a good poking.