MTG Salvation

Under the old convoke rules, when casting a spell with convoke, you could NOT both tap Wild Cantor for convoke and sacrifice it for mana to pay for that spell.

In the section on the new convoke rules announced today at http://www.wizards.com/Magic/Magazine/Article.aspx?x=mtg/daily/feature/255c&page=3, MTG Rules Manager Matt Tabak writes (bold emphasis mine):

So now it is! You don't declare which creatures you're tapping ahead of time, just like you don't declare what lands you'll be tapping ahead of time. When it comes time to pay the spell's costs (rule 601.2g), you can tap creatures rather than pay mana. Note that this is after you have a chance to activate mana abilities (rule 601.2f). This means that if you intend to sacrifice a creature to activate a mana ability, you can't also tap that creature for convoke.

So basically, since it still cannot both sacrifice and tap for a convoke spell, there is NO effective change to how Wild Cantor interacts with convoke?

Correct. There is no functional change for Wild Cantor.

In fact, there is no real functional change for Convoke at all, except that you can't tap more creatures than the spell's total cost. So if you cast Chord of Calling with X=4, your total cost is GGG4. You can pay for that by using any combination of mana and tapping creatures, but there's no way to tap more than 7 creatures to cast it. You also couldn't pay GGG and tap more than 4 nongreen creatures.