short version: Imo EtI+Embers > Petals+Grapeshot, so I agree with PhillyP

long version:

advantages of EtI+Embers over Petals+Grapeshot:
+ with EtI you can either kill with direct damage OR with creatures (for example against Leyline...), so you have more and better options, because
+ you can get Emrakul AND Griselbrand, which attack for 22 in Emrakul's extra turn, or
+ you cast Spiraling Embers, which is better against Thalia, Flusterstorm, Canonist and other tax effects, plus
+ you have all your counters, wishes/sideboard wish targets, Jace...
+ you still have the other kill-variant in hand, if the first somehow went wrong,
+ you can have infinite turns, infinite EtIs, cast you deck infinite times..., you could even use Jace's ultimate...,
+ you have more answeres against several hate cards
+ you could even create a storm count with EtI instead of Petals
...
advantages of Petals+Grapeshot over EtI+Embers:
+ you can hardcast the two cards (which is rarely useful)
+ Grapeshot is harder to counter (but with EtI you have all the counters from your deck in hand to response, or Wish-Overmaster first)
+ you could kill creatures and do direct damage (which usually isn't necessary)
maybe I missed something?

about Teeg and Time of Need:
ToN is really better against Teeg, but there are other way to deal with him also.
A: Wish - ToN - S&T same turn: 4URG or in two turns: 2RG, 2U
(then you can S&T Emrakul and play around Teeg, but you need to run a Tropical and find it or save a lotus petal for it)
B: Wish - Pyroclasm - S&T same turn 4URR, or in two turns: 2RR, 2U
(you need another Wish. In two turns: they could possibly get another Teeg)
C: Wish - Eye - S&T: 3UUUR (even worse)
It seems like Teeg would be the only reason to run ToN, so I don't know if it's worth the green anymore. You could also just try to find a creature without Wish. Anyways, you don't have to cut ToN to play with EtI.

... just some thoughts

btw, I really like Stifle instead of black splash for Thoughtseize atm.