This is a breakthrough and a welcome one. From a end user point of view, it has a couple major implications. First, I believe this reveals the complexity of the parser, which implies a complex syntax, which implies a complex user interface as felt by end users. A more complex the user interface may make it harder it is to attract new editors, although it's unclear (to me) if that is a fact. Second, having an AST repr…
That's the case to some extent, but the opposite is also the case to some extent. Some of the difficulty of parsing is because "ease of human use" has been a much higher priority than "ease of parsing" when discussing syntax, which leads to some constructs that aren't easy to parse with typical CFG-type parsing approaches. It's also designed to be very lenient to ordering and common errors, much like a modern non-strict HTML parser, which makes hand-writing the syntax more friendly and forgiving, but with a tradeoff that the parser has to be more complex, because it doesn't have the luxury of just returning a parse error.