1. Need to run tests, and see where the tear reaches how many stacks, do you guys have access to such information from live Nome?

2. I hit 900-1k stacks on Kassadin a few months ago by 25-28 mins. It also means I got to 750 earlier, but the rate of getting stacks accelerates as the game goes on, so need to decide /when/ you want the items to upgrade and decide based on that.

3. Tear start is getting stronger - tear is getting cheaper, and starting without boots is becoming more viable. You'll only be 25 MS slower than champs with boots 1 and not 50, and multiplicative MS buffs will also give you more, due to the higher MS.

4. AAS and Manamune stack faster than Tear, I'd make the lower figures with the assumption you rush manamune and AAS, so to be a reward for people who've done so, rather than let people charge Tear, get to the required numbers of stacks and upgrade directly.
I'd consider combining this with the double-charge strength suggestion - have each condition charge the item for more mana, but only if you have manamune/AAS, not Tear. This also helps with those who can stack at nexus compared to those who cannot.

average isn't 20 minutes, thats the maximum time it gets, the average should be 15 min game

Why? It's super fun to go around throwing bombs for no reason on Ziggs, for example.

Wow, was about to make a thread about this very issue. Yes, I'd very much like to see TotG and it's build paths looked at for Dominion. As of right now, there's probably only a handful of champions that will ever see the evolved versions of the item on Dom, and they probably wont even be able to unlock them consistently. I just tried building it on Elise in a bot game, as I thought Elise would benefit from the mana shield on the evolved AA. However, even with a spell spamming champ like Elise I was only able to get to 600 bonus mana, despite rushing it as my first item and stretching the game by avoiding capping.

As to what to do with it, lowering the mana cap is one possibility. Maybe you could also consider buffing Mana Charge to add 6-8 mana per spell cast rather than 4. Or perhaps even lower Mana Charge's cool down from 3 seconds to 1.5-2 seconds. Just my 2 cents.

Mine average 20 - 25 I believe and you have to remember, certain champions (AD Malz, Kass) are encouraged by their playstyle to spam spells outside of combat, and Singed.... Well, once he hits a decent bit of mana regen he has no reason to ever turn off his Q.

I believe I've fully stacked tear several times on a bottom laner, and since the maximum stack will drop from 1000 to 750, I'd say leave it as is and if it seems insanely hard to fill (and that kind of is the point, for a free, extremely powerful, item upgrade xP) change it at that point.

Instead of a lower cap, you could have a lower transform threshold.

The item changes to the upgraded form at 300 or 500 mana perhaps, but still retains the ability to charge up to the full 750 as the game continues.

How about just making the mana gain much higher when using spells on buffing allies or damaging enemies? Stuff you'll be doing a lot in Dominion.

In addition, while Tear stays at +4 per cast, new Archangel goes +5 per cast so after Arch, another thing that will make it charge faster.

On the other hand, Manamune is changed to get +4 regardless whether it's basic attack or a cast/spending mana. IIRC the old can charge +5 max every 3 seconds if you keep up both casting spells and auto-attacking. On the other hand, auto-attacking makes it charge faster in the new one.

@SuperExplosion: Reading the descriptions, it seems that Seraph's Embrace has a fixed "+1000 Mana". Meaning, if it transforms at 300 bonus mana, you end up still end up with the max 1000 Mana (250 base + 750 bonus). It has to be changed to inheriting from AA for that to happen.

To be honest, I am more afraid of these items more than ever now (given who their current users are).

This is primarily why I'm reticent to make the change.
I don't want Kassadin to get even more nuts with an activatable shield. I'm not too worried about Manamune though, as it's much better on RADC than bruisers and melee.

Fun fact about tear (right now as it stands in live) and everything it uses (AA/Manamune).

The tooltip says 3 seconds but you can spam skills as fast as you want and you'll still get the mana bonus. There is some strange threshold where you can spam 3-5 skills before you even notice that it has a cooldown (the items have cooldown things now) and it slowly builds up to 3 seconds.

Is this fixed in the newer items being made?