Something to think about:
The S3 versions of Manamune and Archangel's Staff "evolve" into new items once you've obtained the maximum of 750 bonus mana, gaining some pretty cool new functionality. However, it's unlikely that you'll be able to hit that cap on Dominion. Is it worth having a lower cap for Dominion?

I think so.

Usually I end the game with around 700-800 charges on Blitz, and even AD Malz who STARTS with Tear only reaches full stacks near end-game, like 25+ minutes in.

Probably should drop it down to 200-500 stacks, yeah.
I'll leave the exact number open to discussion.

Yes. Most games will last only what, 15-20 minutes on average? If AAS takes about 9 minutes to evolve on a Singed keeping his gas on, most people won't ever hit the cap, or even then their functionality will serve all of maybe 3-5 minutes late game should they hit evolution.

Yes, Dominion versions should have a lower cap. I have yet to(or see anyone) get much more than 500-600 charges on a Tear in Dom.

I'd be very worried that that lowering that cap enough to make them viable would make them broken (for Muramana at the very least). You don't need sustain in the same way and I could see the active causing some serious problems with bursting in the fast paced environment

Most champions will hit 750 by endgame if they purchase Tear as a first item. Champions like Urgot and Karthus get about 100 stacks by spamming Q waiting for the game to start. 75 seconds for 100 stacks under optimal spamming opportunity.

A better limit would probably be 500-600 so champions don't need to spam or buy it as a first item in order to hit it, or possibly have it even lower and then also have the cooldown on the stack generation higher so that pregame spammers don't have a significant advantage over champions that require targets.

(That said, I still prefer Catalyst start over Tear if I need mana)

Well the issue i see is that the mana on a lot of the mana items like ROA and AAS and FH have gone down and cost gone up. This is quite a big change for manachampa such as blitz and ryze. A secondary is as mentioned, that seraphs embrace wont see much, if any, use on dominion. Its a sweet item but would take much too long. In an effort to stem a huge spike in mana capacity once the 750 limit is hit, i propose that the increase in mana per spell be upped, but limit shifted back to 1k

To be honest, I'd kind of like to see the Dominion versions have small cdr added to them, to make them easier to build up - and then keep the cap the same.

Basically, the problem is you either have to buy tear as your first item, or you don't buy it at all.

Do we want it to have a lower limit, or charge faster? I guess letting it charge faster would just help already-powerful champions like Kassadin.

On that note, could we get Rod of Ages' charge time lowered at the same time? 10 minutes is an eternity in a dominion game.