That's a really bold assumption to make. I'm pretty sure it wasn't just the Unity Ruleset debacle that effectively killed Brawl. There were numerous factors that contributed to that, including the growing existence of us at the time, Project M.
See, here's the problem with saying that if we don't stay with L-Cancelling, we're going to "sever the community": the community was already severed the moment PM was abruptly finalized. There are a considerable number of people now trying to say that if we want to continue having events, we'd be best off having 3.02 tournaments because that was "the best version." You and I both know that's garbage based on very faulty observations of the period, but way too many people have been saying we should've either made the components of the dev build available for play if the community finalized them, or gone back to a prior, "better" version, like, say, 3.02.
What's going to do us in, then, is something completely unrelated to L-Cancelling itself: it's a lack of community unity, that stems from two distinct parties. There are people who want to change things because now is a better time than ever to try, and those who don't want to because they want to save something they actually can't articulate.
I'll admit wholeheartedly, as part of the "change" movement, that there's always going to be a chance for failure, and that it's reasonable for there to be fear of that failure. But you do also understand that what fractures the community in this particular circumstance wouldn't be auto-L-cancel itself, but the refusal to even give reasonable consideration to those changes? That, to a similar extent, refusing to make changes could also, in a way, cause the death of the community due to lack of new player integration?
It's more of a situation of "how do you know you won't like it if you haven't tried it," and to be perfectly honest, I highly doubt anyone who's vehemently against it has actually participated in an auto-L-cancel tournament. Because it comes down to, unfortunately, this culture of stubbornness that has been developed in the Smash community.