Well... the man can think pretty big.
I'm definitely not writing this guy off. In 14 years SpaceX has gone from a garage startup to reusable orbital launch vehicles. He and Bezos have thoroughly disrupted a stale aerospace field that was perfectly happy using Atlases forever. For that alone he has to be given a lot of credit.
Funding this particular project is going to take one hell of a sales pitch, and indeed, I'm already seeing this described as just the beginning of a fundraising effort that will last for decades. Getting to Mars is going to take a repeating cycle of sales pitching, fundraising, technological success, and perceptions. It's certainly helpful that Musk is already putting 5% of SpaceX income towards the Mars vehicle and has already built a carbon fiber fuel tank, one of the key components. In fact, a lot of what he showed is already existing tech, especially the Raptor engines and booster return. That takes a lot of the uncertainty out of the equation--it's just a question of scaling up.
On the other hand, SpaceX has been pretty aggressive in the past with launch schedules. For all the success that they've had, IIRC they're at least a few years behind schedule. Liveblogs were noticing that the timeline Musk put up today was already impossible given the recent Falcon 9 failure on the pad. Will the Mars vehicle still be viable if you push all the dates out 5 years? Maybe, maybe not.
Lastly, I hear they're naming the first Mars vehicle the "Heart of Gold". Improbable indeed! (At least it wasn't the "Kobayashi Maru".)