You could be onto something here...
There is also Zoro's line - I always wanted to have a flaming sword...
Not sure if that was the correct translation though.
I'm pretty certain of the Solid, Liquid, Gas Stuff
CoO is Solid Haki --- Fixed Shape - Fixed Volume
CoA is Liquid Haki --- Non-Fixed Shape - Fixed Volume
CoC is Gas Haki --- Non-Fixed Shape - Non-Fixed Volume
Meaning the reason CoC is Rare is cuz Users cannot change their Haki's Volume
The best They can do is turn it into Liquid (CoA) to move it around (Basically controlling it's Shape)
But CoC Users can turn their Haki to Gas Form, hence why it's released like a Gas Bomb & can Invade their Opponent's Bodies
(And Free Volume symbolizes Freedom, so you could say CoC Users have a Free Haki)
Advanced Haki Techniques are simply mixing of these Three Skills
Resulting in each Haki State having Three Advanced Techniques (Such as CoA having Hardening ---> Barrier ---> Internal Destruction)
CoO also have Three Advanced Techniques & same for CoC
But outside this Solid, Liquid, Gas Forms, Haki in it's Original Form is a Flame
And yes Zoro did indeed say He likes idea of having a Flaming Sword
Also Shanks does have a Flaming Sword, not to mention Usopp lying about Zoro unleashing Flames so it has to come True