1) I'd love to merit with a SMN. I think SCH and SMN work well together, we cover each others weaknesses very well. SMN can hastega and receive weather, and with SCH there, DDs have absolutely no reason to hold back with seigan and /nin. Now with the new buffs, maybe SCH can be accepted as a healer. 35% AoE haste, 1 atk buff + dia2, double attack, and 100% offense from DDs, oh yeah and lol +7 Str. But I'm just a silly SCH with a dream...
Smn and a Sch in one party (as is) would be overkill. Good Sch can keep the entire healed as is, and they make claims of being able to allow all DD's to go /sam or /war and go balls to the wall, which they use as an argument to overcome no haste. I've yet to merit with a Sch healer, so I can't confirm nor deny that claim.
Smn, can also keep the entire party healed and hasted on their own and also use Rages as well. There's really no point (as is) to have both in one party. Each of them separately would benefit more from a Brd, Cor, or Dnc than they would a Sch, or Smn. Now, Smn's more common issue now, is we require everyone to use /Nin to be safe and smooth. It's gotten to the point now, where people have realized Whm and Rdm are both able to support a party while allowing War's to /sam, Sam's to /war and Drg to /sam. Because of that fact, people are a lot less likely to settle for a Smn or Sch as merit healers these days.
Moving on to the update and 100% support role...
Smn/Cor with Ifrit Favor.
Assume you're spamming Crimson Roar every 1:30 (again I'm assuming double BP timer) and using Chaos Roll, as well as the expected 18% Double Attack from the favor.
We're looking at 18% Double Attack, BP ward's 9% Attack plus /Cor's Chaos Roll's Average 8.2%*
18% Double Attack & 17% Attack.
That would put us dead even with Corsairs for front line buffs, assuming they were using Fighters(DA) + Chaos(Att).
But... Cor can Deal more Damage than a Smn, and with zero MP cost.
Cor can offer Refresh to the back line, as well as hMP or Exp bonus.
Cor can also reliably and quickly sleep a mob.
Cor can also (not optimally) act as a puller.
So even if you wanted to make the statement that a Smn could keep up with a Cor in Damage, the 3 other remaining factors will still justify everyone choosing a Cor and Brd over Smn. Haste is not something we can offer a party unless the main healer is a Sch or Dnc. From a Sch's standpoint, maybe a Smn becomes the #2 option second to Bard. Dnc main healing... Is what I consider an exotic party that you can't make a basis on, along with drg/whm parties. Pre-update, I'd also venture to say that a Dnc was a better support job than Smn, assuming they have 5 merits into Haste Samba. Post update, I'd have to guess that for the typical merit party Smn would be ahead of Dnc now. But Smn can still offer Mana Burns something. * /Cor Chaos Roll average is based on the theory that you'll Double up on 1-3 and 5. Leaving a possible 4,6,7,8,9,10,11 result, 12%,6%,7%,1%,8%,9%,15% respectively. Combined = 58. 58/7 = 8.2% Attack on average.