John Gruber hasn’t “abandoned” Markdown. He just doesn’t want to add anything to the core language. I’d be supportive of names like Common Markdown or Standard Markdown if this was just about clarifying the standard, but you can see here that this isn’t standard Markdown – It’s Markdown with some extensions built in. It’s entirely reasonable that Gruber wants “standard Markdown” to be Markdown without any extensions.
And to be clear: I think this dialect is a good idea, but it’s not standard Markdown (and “Common Markdown” still sounds too official). I think this should either have a completely new name which makes it clear that this isn’t The One True Markdown, or be split into clarifications of standard Markdown + extensions.