I am of the firm belief that the ability to reroll perks on weapons and armor would enhance the character building experience and allow players to design more specialized builds.
However, I do not want god-tier rolls to be [i]too[/i] easy to obtain.
How do we go about rectifying these two conflicting philosophies? Simple, copy the system used in Diablo III and The Division.
In both aforementioned games, you are allowed to pick [b]one[/b] stat to reroll. You may reroll it as many times as you like, but it can only ever be the one stat.
This would translate to Destiny as thus:
Rerolling can be done at the Gunsmith for a cost of [u]2000 Glimmer[/u], [u]20 Weapon Parts[/u], and [u]20 Legendary Marks[/u].
Upon selecting the reroll interface, you would be asked to select an equipped Weapon, Ghost Shell, Armor Piece, or Artifact. Upon selecting an item, you would continue to select [b]one[/b] of its assigned perks. After selecting a perk, you would be given a list of all possible perks for that slot with the option to click REROLL. Clicking the REROLL option gives a confirmation screen, warning you that continuing will not allow you to select any other perk on the item on further rerolls. After confirming, the game will reroll the perk, allowing you to select [b]one[/b] of three perks from the full list of potential perks for that slot.
I think that this would enhance players' players ability to tailor gear to suit their preferences, and would allow many otherwise exciting drops marred by one poor perk to be improved upon.
I would prefer a means of changing perks on the gun. Example you have to get another copy of the weapon with the perk you want and then have a moderate cost to replace a perk maybe 150 marks or require glass needles. This should increase the value of loot. As for one god roll to rule the arch type this is imho an issue with perks themselves. Once there are enough varied and beneficial perks variety can be achieved. Reroll will create balance, but improve the perk pool will create variety.