No he didn't. Sakurai said nothing like that about 3rd Party characters during any direct, otherwise we wouldn't have Cloud.
He said appearing on a Nintendo console would be nice but isn't a rule, which even then isn't close ties to Nintendo.
Playable isn't important, even then he was one of Generations first really good mods on PC along with Metal Sonic and Amy.
Beyond that, he was a main character in the most loved 3D Sonic game, Sonic Adventure 2, which was also one of the first Sonic games to appear on Nintendo consoles along with Sonic Advance.
As much as I like Classic Sonic, I don't think so. He'd be a little boring as a choice and we don't know if Echoes have to share proportions with the base character yet. Classic Sonic is a head shorter then Sonic with shorter limbs and it's not like you can make him faster or stronger then base Sonic to compensate for that shortcoming, thus making him worse then base Sonic.
I feel the best choices for a Sonic echo are Shadow or Metal Sonic, both have the same proportions as Sonic, can use the same moves, add another character, and are massively popular, though Shadow more so then Metal Sonic. Shadow can share stats while Metal could be faster but weaker or harder to control.