after thinking on it a bit
+ makes things easier to balance. it's also mentioned in the article that they want to get away from "whole archetype" balancing and be able to precision balance individual weapons. you know how the gun will work no matter what situation with locked rolls.
+ instead of having a double roll (getting the weapon, then getting good perks) this means collectors only have to worry about getting the gun itself, could lead to more excitement or caring about certain weapons vs "hey, i got awesome weapon.. aw fuck it's got kneepad and icarus *shard*
+ could make it feel like less of a job to grind for a good roll on a weapon when the weapon just drops
+/- this was probably needed with the two-primaries change to the sandbox. Some rolls on two different primaries could combine to be super OP when put together, which would be insane to balance. fixing the perks makes this change easier to deal with at some cost to the player base cooking up some primary combo recipes.
+/- instead of having some weapons with lots of potential perks, the same effect can be accomplished with just making more weapons where some of them have shit perks, so it could just even out
+/- along with the change to 4v4 pvp and this change, Destiny is definitely veering back towards more classic Halo sandbox design. people may or may not like that
- brings into question the worth of getting duplicates of the weapon. right now shit rolls are basically always destined to be mats, but you have a reason, because it's shit rolls. just getting a duplicate might be a bit 'meh'.
- does take some of the lootiness out of the game for people that like that. as above, they might just replace it with having more guns anyway.