It was also a rule that was quite good against Tohaa. Then nerfed so it would only remove the armor. Then removed entirely... just being impacted, regardless of you passing or not the TS, meant getting burnt, so it was not so clear-cut, I'm afraid. Tags used to get POSsessed and then forced to take a big jump to break (since falling from past a certain height meant continous damage...). Falling damage was removed in N4, yet continous damage remains. Perhaps we could get that rule back too so the TAGs can get wrecked by splattening them instead of just E/M... /sarcasm off ;)
Tohaa's Symbiont Armour being specially vulnerable to Fire was a different rule, unrelated to the Burnt state.
Burnt state required "Fire" rule, now called "continous damage". The mechanic also bled over to fall damage, and the fire type of "ammo" bled over to the Tohaa (symbiont armour) vulnerability (which in the first change meant a buff for all 1 wound symbionts and an almost zero playtime for the Gorgos and the Ectros, since a single impact, regardless of ARM roll, would mean losing the symbiont with all remaining wounds in it). My point is, in short, that cherry-picking is a little one sided. In the end, the really vulnerable troops to the burnt state were ODD and TO troops, who would lose everything, with camo troops being downgraded to mimetism-3 which was not all that traumatic since they could perform (if they survived at all, that is) without the marker state to a degree.
It's not "cherry picking": OP mentined that he liked one specific rule ("burnt state") because of what it added to the game, and a few others (like me) supported the idea.
Not cherry picking, this is about the value of the rule and not how it was implemented to the letter. If it comes back (and I really wish it comes back) it could be implemented in a different way, like affecting any level of mimetism, not affecting camo state, being limited to very specific guns or ammunition etc.
Doesn't need to replicate the curiosities of N3 fully, where the reason it didn't work on mim-3 was that it was the lowest level of Camouflage and Hiding skill, while ODD was not part of that skill set at all. It can simply be a state that "Prevents the user from entering marker states or benefitting from mimetism or albedo"