Possibility for double retaliation
As a grenadier engineer in sPvP (typically only managing for 2-3 seconds at a time), I will respond with an immense GODJESUS YES RETALIATION STACKS
It’s most obviously exemplified in WvW when, say, grenading a group of players in front of a door who have the retaliation symbol on them. Ow 3k per attack.
Also, this applies to chaos armor / flame shield / etc. Chaos armor is a major issue against heartseeker thieves – as when they steal from me, they get Gunk, which makes a field that creates chaos armor when they leap combo through it (HEARTSEEKER), and makes my grenades give me 3 random conditions and them 3 random boons every time. It really is a complete nightmare.