while i can agree, and in someway, miss upgrading options for the white and blue gear, which.
What you can use it for atm, is two things imo, One to lessen the strength of a character and create challenge if there is none to be found with certain builds and gear etc.
Two, is using it to learn the game and somewhat figure things out with less affix’s involved for those learning in game, new to D4 or something like that, perhaps wanting to try out affix’s for free and for cheap. Obviously SSF is involved here.
That all said, I miss the fact at the very least we could “mw” upgrade the old blue and white gear to 5 stars. and part of me misses ancestral blues since they looked cool with the effect imo, making a blue ancestral was kind of fun.
and I miss sacred items. So while function is overall better, I hope they add back into the loot at some stage, it makes sense to dial it back atm though until things are sorted better.
While I like your thinking, the problem i see, is that if you allow that, it means spending more mats for little gain, why would i turn a white to blue etc, if i cannot temper, and since finding rare is easy and printable, and leveling is fast now, even more on alts and if i have obols or gold i can skip blues.
That is the problem, in the old slower game, it was somewhat more viable to upgrade blues and whites if you wanted to save mats, but now, what you propose adds a crafting train to the game which is interesting for sure, however obsolete and players won’t use it. I mean the didn’t use it before as much as it was.
I think I don’t really want more time crafting as is, I think the crafting needs to be not overly time consuming, I don’t think a arpg should be too much like a mmo.
Instead I think Ideas like the cube, weapons with charges, magical powers, cursed weapons, throwing knives, idk things like that would be a better way to use other gear,
SO for example its a blue item, and casts lightning pulses or whatever, and has 50 charges or maybe perma, special effect, perhaps it can be upgraded with a temper or simply MWorked with a out of 5 cap or something.
Just spitballing but that is what i would bring into the mix, adding to the bottom tier crafting chain , was basically already done and skipped over by most. 
If they did something about trading, and gifting items, this would change the game.
I only play SSF and normal legs and unique will be used when GA doesn’t drop and isn’t a useful GA, So yeah , it’s like designing too different games when you are not a mmo, but allow mmo like trading and gear buying which is the issue with mats and boss mats also. I can tell you no mythic come easy and I play more D4 than i would actually want to, and use all seasonal bonus boss mats and get nothing.
So this needs to be looked at imo, it would feel like two different games imo.
The problem with adding crafting to GA items like you describe it then you take away the joy of finding a GA drop, This game already suffers this issue, i decked my alt in Uniques and even my main somewhat spamming the obol trader lol, that was kind of lame ngl, but it saved me time lol
you want to find items in the field in diablo, and sometimes at a vender, D1 the blacksmith would occasional have a unique item for sale for exmaple, and so you may make a choice to hunt some gold to buy it, or you may not.
D4 obols rain and you can spam the trader and get great loot lol
So this game need’s to sort that out first imo. Nothing is exciting about a GA drop if i would otherwise just craft one.
Tempering solved a sifting through affix issue, which was needed, and allows some build options, but the core of loot in a diablo imo, is choice and finding a drop that is powerful and a upgrade, becasue it’s rare and exciting, but should be exist withing reason, which makes me not enjoy the odds and the target farming for mythics for example. I mean my main could have seen atleast one mythic by now and i would have felt joy rather than what is the point and looking up at a huge mats mountain to even target farm them.
good thoughts, not knocking it, I just have a different view, but I do agree the pool needs more spice, and to feel more diablo and less, mmo-like.
