I would love thematically specific Destroyers for each legion. I guess not all Legion Destroyers used the same tactics and/or weaponry. F'rex I can't really guess how IF Destroyers would work given the character of their Primarch (Though after John French's The Will of the Legion I guess he wouldn't mind a bit of cruelty). For me any flavoured rules would be good, even if they're not 100% balanced. But I'm more a narrative player than a competitive one, so I understand the objections.
Even so, I think Destroyers need some love. Lorewise they are described as bringers of utter destruction with a varied arsenal of Old Night weaponry, but rulewise they only have rad grenades, phosphex bombs and rad missiles. Kinda meh TBH.
I think we already have this. The legions that embraced Destroyers have that reflected in more specialized units (effectively giving them two types of Destroyer units) and/or access to Rites of War which emphasize the role of Destroyers in army composition and give similar 'scorched earth' effects to other units. The Imperial Fists work exactly like default-Destroyers because that's what they used them for; there was no expansion of their role or requirement for special equipment. Need rad or phosphex? Deploy Destroyers, let them poison everything and then move on.