In general it’s a good idea, but it’s nothing new. Sites like dslreports.com and SpeedTest.net have been measuring speed and providing diagnostics for years. The BitTorrent test however isn’t replicated by many yet.
One thing that isn’t addressed is how they will detect if an ISP is adjusting their routing to handle M-Lab servers specially. What stops an ISP from not throttling from one of Google’s “36 servers in 12 locations in the U.S. and Europe” but throttling all other data? Perhaps Vint Cerf and friends have a plan in mind but it seems to me this could be a cat and mouse game.