I don’t think the deck will be there next year.
By that I mean the deck as we know it today.
Some kind of spell (quest) mage deck will exist, but I think it will play a lot differently, both for the mage and for people playing against it. People may still hate it of course, but it’ll be for different reasons.
Consider incanter’s leaving. Incanter enables the mage to do RSW or cram session (latter is also rotating) into more spells, and as those spells were also discounted by incanter’s, the mage is likely able to play those as well.
From what we know today, that won’t happen with siphon.
edit: closest you can do with siphon is first draw cards, find that the cards you’ve drawn is exactly what you need, but they’re missing that 1 mana discount to be playable this turn, oh but you happen to have a viable target for siphon to apply a discount. And you’ll have to do this with RSW always costing 5, not 4, so deciding to draw first before siphon is another decision. That’s a lot more conditions to fill than “did I incanter’s before (on 3?)”
All this is assuming mage can consistently get off the honorable kill effect.
Well, a cheap spell may be the thing you cast early game to charge up the mage weapon. A cheap spell gives you some control on when you trigger the discount (play it when you’re 3/5 or 4/5 charged)
For extra greed run stormpike, mainly to discount the owl, so you can cast a discounted big spell followed by a discounted owl that repeats that big spell.
I think the bigger problem for big spell mage is whether there will be good new big spells, especially for after rotation.