[Season 6] How viable still Book of Thoth?

As probably everyone knows, Book of Thoth ( ) was large used by mages during season 5 and became almost a core item on magical gods looking for power due the High power and high mana it provides.

However, now at season 6, Hi-rez is trying to make this item "less core" but also keep it viable, they change its passive to convert mana in power only if the mana was provided by items (including itself) and to compensate the change, they increased the conversion percentage.

Also his T2 was nerfed to contain people rushing this item and gaining too much power early game, so blessings like Mage's Blessing returned to shine.

But the question is: does Book of Thoth still viable in almost any mid laner? It's viable rush it or finish boots then return to finish it? Or this is an item that does not worth build in any mage anymore?

I believe Book of Thoth is still a viable option that, if you're going to stack, it's way more worth it then Warlock's Sash. Just from the item alone, at max stacks, you're getting 80 damage + 90 from the passive, and also it gives you 1000 mana, which helps you stay longer in teamfights so you don't have to back for mana.

I would only build Book of Thoth on Kulkulkan or maybe Scylla

Why? Gods mana hungry like Poseidon wouldn't it be good?

That makes senses.

I think the item very much depends on a few factors.

1. What are the important stats for the mage? If they really benefit from early aggression and can effectively use Bancroft's Talon, or want high early CDR and thus want to go ASAP into Chronos' Pendant, then maybe they don't want to get Thoth...or they'll want to delay it significantly.
   
   
2. Are they strong early/late, and are they willing to delay early strength to get to late game?
   
   
3. What's the matchup? Is it clear they should play passively and mostly just clear wave in early laning? If so, Thoth might be just fine.
   
   Alternatively, do they have a generally even matchup, or an advantage? If so, getting something that allows them to be aggressive might ensure their early lane dominance, whereas getting Thoth might mean you lose that advantage.
   
   
4. What's the scaling on their abilities? High scaling means they'll likely benefit more from Thoth, at least late-game. High scaling is a late game stat anyway, as you get more and more high power items.
   
   
5. How is the rest of your itemization gonna go? Are you getting items that increase your mana to take advantage of Thoth's passive?

So it can still be worth it, but like I think the HR people said in the patch notes show, it's forcing you to plan ahead and itemize based on intention. If you get Thoth, but the rest of your items are utility and not much mana, and you won't be considering things like Book of the Dead, Polynomicon, Soul Reaver, etc., then it might not be worth it.