Steel case can and has been reloaded, even done a few myself to prove it.
But I would not plan to do so as its more work than its worth.
20k rounds through your AR of steel case or standard brass and you are going to be looking at a barrel, as premium accuracy will be gone.
Bi-metal aka copper plated soft steel bullets will wear and erode the barrel faster than copper or lead core copper bulets, but if you have the means to put back 20k rounds of 5.56, you can probably afford to put back a barrel or two.
Something we should all think about, especially when barrels are so cheap right now.