This might be an unpopular opinion, but why isn't there a Lascannon for the heavy gunner class? Having an ultra-heavy single target focused or Line Based AOE weapon specialized in taking down Extremis class enemies for the heavy gunner Seems rather appropriate to me. It's a rather common weapon for space marines, but the game seems to lack it entirely. Just an Upscaled Las Fusil with lower Ammo, and longer charge times basically, would make clearing hordes a pain, but would make the War Stomp melee attack more prevalent for Lascannon builds.

Any thoughts on this for an intelligent debate on the pros and cons of the inclusion of this weapon would be fun, if anyone would like to join the discussion here.

Are there plans to add such a weapon? I have not really been following news for the game much as of late.

​There is no Primaris unit with lascannons yet, that's why they didn't make it

Primaris isn't the only space marine type that use lascannons. Devastators use them as well, and the role of the heavy gunner in space marines 2, and the Heavy Weapon specialist of a Devastator Squad are basically Paralell, As a matter of fact, I would argue (despite no actual confirmation one way or the other, that Straben "is" a Heavy Weapon specialist, and could fill that role "in" a devastator squad. He's certainly no Primaris, and thus can't be a Heavy Intercessor as that would require him to be as such as far as I know. (My Warhammer 40k lore is fuzzy in weird spots, apologies for that)