Yup, melta. If they can fire alternate muntions, they should be able to do melta. At least the bigger impaler weapons.
Tranth's specialties are haywire, stealth, power armour, and Titans. Unless you want him to only ever study those things, that is not a good argument.
No, his specialities are psytech, gravitics, and maybe stealth after a bit of work.
Because fundamentals, DAoT treaties, and major human powers being just better at anything that we don't have a unique advantage for.
I am all for grabbing some low hanging fruit, but melta against Tyranids which
might happen to work well against these Tyranids (Necron gauss weapons have ridiculous AP, so I would bet that they would work even worse than against normal Tyranids) along with a assumption that they could work with Impaler specialist munition?
Also, they would be specialist rounds, rare and expensive. Nothing remotely anti-horde.
And this instead of a DAoT superweapon? When it can, at the very least, slow or accelerate entire fleets and we will be playing keep away with them in the Void?
Also Melta are Advanced fundementals, so we could have Pulse Weapons, Cogitators, Strike Craft, Torpedoes, Normal Genetic Engineering, Armor, Shipbuilding, Torpedoes, or Advanced Material Production instead. Or much more.