Yes except there would be no reason for players to move forward. If they are already content with what they have then they will see no need in grinding the new content or grinding for new gear. Which means less people playing and less time spent playing. Do you seriously think Bungie will allow that to happen? They might very well allow you to upgrade old weapons, but the means of doing so will almost CERTAINLY be in the endgame so you will still be forced to set aside all your old gear and grind to get new gear to replace it in order to be able to do the end game content.