i think, some of the charm got lost, when the golden uniques turned into orange legendaries
now you want to take the special effects, that makes legendaries so special and dispense them over all other rarity types
thats no issue at all, since it greatly helps, balancing the itemization and makes rares and magics viable again
the problem is again, an authentic one
legendaries are not legendary anymore
since they appeared to not even have special fix stats in D3 and just provided those cool powers, i think, you will do the same in D4, which would eventually just make them the same as a rare with a legendary power crafted in it
so the whole rarity type becomes meaningless and is only there to “educate players about affixes and effects until endgame” thats not, what a super rare type of item should do
so my solution would be, make the “legendaries” “uniques” again
give them golden font (because it looks better) and dont give them legendary, skill altering powers (the consumables have them), but just very strange, alternative stats and affixes, that you can only find on them
like a lot of walk and attack speed on a single item, but nothing else, so you can just go crazy
or even immunities or very high resistances
make them UNIQUE but not superior
fun, usable in certain builds and playstyles but not mandatory to clear the endgame
and then you can also craft those legendary powers into the unique items, since they arent better than the rares, by default
just very special