We haven't encountered the problem yet in a game I'm playing in where we're 9th level (well, there's been a couple issues of "I can't attune anything else" but other party members still had "slots" open.)
My 5E conversion of Rise of the Runelords required the PCs to make some tough choices near the end, but part of that was I was a mean DM and ruled the items they needed to enter the BBEG's stronghold required attunement.
My 5E conversion of Rise of the Runelords required the PCs to make some tough choices near the end, but part of that was I was a mean DM and ruled the items they needed to enter the BBEG's stronghold required attunement.