So we have the bolter weapons. They fire different kinds of bolt shells and that's okay. But what about plasma? Sure there are things like enhanced cooling vents and stuff like that, but how do we actually show that?

My answer is purity seals.

Yay or nay?

I don't see the point in showing the upgrade with purity seals. At best a gun would have one on him but not much more. Plus with the heat of the plasma gun I'm not sure the seal and paper will last long.

I like how Space Marine did it with changing part to gold or adding small details.

I'd like a Plasma mod that adds Ablaze ailment at the cost of max ammo or increased overheat.

I'm not asking for several, but some mods like increased magazine capacity (meaning reduced heat build up) can be potentially more difficult to display on plasma or melta weaponry. It's not just another drum mag and making it something like different looking coil models takes modelling and QA for clipping, etc. You could always make the coils a different color too, but it feels like that should be reserved for specialised ammunition like a heat ailment ammo. A purity seal model already exists and would be a good way of visually portraying the gun is not of stock plasma gun quality. Indeed it is in fact a blessed weapon, a status achieved through its accomplishments or its sublime manufacturing.

Okay, I see what you are meaning and I'm totally for it. But for now I would prefer the team to focus on Eldars, they are definitly forgotten when it comes to weapons visual modifications. I think we already had enough visual improvements for our faction. For now.

Not saying the Eldar don't need some more mods and corresponding visuals. Just saying I'm a space marine player and what I know is they put holy stickers on everything.

Yeah sure but what I mean is that the team is heavily focusing on us, I mean, at each update we got sometimes some cosmetics, but Eldars ? Not that much. For now there is already a huge inbalance of cosmetics and personalisation between factions, even if some of our cosmetics and visual effects are really shitty (Master crafted stormshield, I still do not like you) but orks got their unique sitting animations and aiming on edge very recently after waiting for it for months, and eldar are still waiting for some smoothing in some animations. I think we should step back for a moment about cosmetics, we already got a lot even if it's not very satisfying compared to what we see in Warhammer 40k normally, but some other factions could actually benefit about having some attention paid up to their animations and look.

i would argue that a purity seal would indicate master crafted more than a cooling vent ..
a cooling vent can just be a .. cooling vent somewhere on the side or something..

The cooling vent on the muzzle already is a cooling vent. And also we have different models for the master crafted versions, the seal just means it is blessed because it does a do better. Also a modified muzzle vent would require more work than attaching a purity sticker, the point was to make a quick and cheap solution.