Switch Python's parsing tech to something more powerful than LL(1)

Query for the parsing wonks here: would an alternative parser make it more viable to support “context-dependent keywords”, like async/await were in 3.5/3.6, and like JS uses for all new keywords?

I’m wondering because @guido raised the concern that inability to add new keywords might become a blocker for pattern-matching syntax. And in retrospect, making async a keyword in 3.7 turned out to be pretty painful.