Quite true. I assumed it would be eight teams in each conference, with the wild card play-in game for the bottom slot.I've never seen an American sports league expand its playoffs, then contract them years later (2020 weirdness excluded). We're stuck with this system, and I'm sure MLS will find away to expand the playoffs even further at some point down the line.
I like the rest of it, though. It's a tweak, not a massive overhaul of what we have now. And MLS would get two opportunities to sell championship merch rather than one for minimal additional cost.
Another angle: the Opening Day match of the following season between the Supporters Shield holder and MLS Cup holder could go on Fox's air to drive MLS Season Pass subscriptions.