One of the best things that I can think of for r/m/es would be a quest to get an ammo with a latent effect on it. You need to have the lvl 99 version of the weapon to start the quest (afterglow not required). The ammo would basically offer the exact same benefits as your r/m/e weapon, but as a latent effect (latent triggered by not having that r/m/e weapon equipped). The relic/emp versions would also give access to that weapon skill, and the ws will get the same aftermaths as if you were wielding the actual r/m/e, whilst the ammo is equipped.

Un-equipping the ammo, kills any aftermath that was active and removes any hidden effects or stat bonuses.