Interesting new revelations from Mod Rowley:
"Death guards (main hand) are siphons (lower case 's') - it functions similarly to The Siphon (capital 's') in that it takes energy one one place and puts it in another (albeit more concentrated).
Ditto the off-hand is a conduit, not The Conduit, which connects your current location to the Underworld, so you can conjure spirits.
These are categorical terms, not item names - i.e. to conjure spirits requires a conduit; to harness necrotic energy requires a siphon. This way, we can later on have different weapons other than death guards and underworld lanterns, akin to melee weapons having maces, short swords, 2-handed swords, spears, et al."
https://www.reddit.com/r/runescape/comments/14ynd9s/comment/jrxbd2j/?context=3
What Mod Rowley previewed is we are going to have weapon specs with the Necromancy Mains and offhands. Perhaps we can have different Necromancy weapon specialization through future expansion of Necro Skill Tree.