Looks like Bungie listened to what community had to say about armor sets in Destiny 2 and they are adding seasonal mod slots to them.
Studio announced that in April seasonal mod slots will be added to 17 armor sets in games world loot pool.
As you might know, with the new Season of the Worthy, bunch of old sets revitalized for armor 2.0 and added into the world loot pool, this means that these old armor sets can drop from pretty much anything from anywhere. But problem was that these sets could not use any of the seasonal mods, and this was concern that players had. since he desire to use old fashionable armor clashed with the need to use strong new armor, and this rendered the returning armor pretty worthless.