In order to upgrade your Exotic item to the next Tier, you should have to max it out, and wait for Xûr to sell the upgrade for your particular item.

This upgrade should cost 2 shards instead of 1, and reset the last 3 nodes while leaving the damage/defense the same.

For example, let's say I have a maxed 331 Gjallarhorn and the new damage cap is 362. I buy the upgrade from Xûr for 2 shards and ~7,000 Glimmer. The last 3 nodes are then reset, but the weapon damage stays at 331, so that when the last 3 nodes are upgraded again, the damage total is 362.

I think this is the most reasonable approach, because I for one hated having to re level Icebreaker, Gjallarhorn and Thorn from 0 after maxing them, and cannot be bothered to do the same for the 8 other exotics I have.

No way I'm doing that shit again in 2 months.