That is an indeed not very pleasant thing to hear about, HC lost one of it's unique attributes due to this fact... looks like Ascaron made so that the HC and SC servers share item files between them with no restrictions applied... Why can't they revert what they had before? The SC and HC servers should have always stayed completely independent from one another, the same environment we had with S1.
With that said, allow me to suggest one thing or two that would allow us to have a safer HC experience...
As Antitrust pointed out before, item coloration would not be a bad idea after all, the thing is they would have to make it a way that doesn't confuse the player.. (WHILE IN THE CHEST) let's say making SC items look light green and HC items look light red.. then when on HC you try to equip a HC item a message would appear saying " SC Item Only" and vice and versa..
or.. another way would be making the the SC item greyed out and unusable on HC and vise versa .. doesn't matter the exact way to do it, as long as it is implemented ingame.