Personally, I'd like to see his enthusiasm more focused toward space megastructures, such as O'Neill Cylinders and Dyson Swarms. It seems to me that humanity would benefit a lot more from mastering industrial-scale manufacturing and construction in space than sticking ourselves in another large gravity well.
Economically, I consider this inevitable personally. The very tech you need to get to Mars with anything significant is this tech, and for quite a while, there's going to be more of this stuff in orbit than anyone on Mars.
Plus there's a non-trivial overlap with what you need for a self-sustaining Mars. We know we can build a functioning supply chain on a planet rich in resources; the real technological question remaining is, can we build a functioning supply chain out of nothing but energy and the requisite atoms not already preconfigured in desirable molecules?
BioSphere was interesting and all, and this Mars shot is interesting, but if we really want this kind of technology, what we really need to do is to build ourselves a base in Antarctica, with the goal of producing a base that can build a duplicate of itself with no additional outside resources other than what the base itself can scrounge from the environment. (With possibly a couple of carefully selected exceptions; we might spot them some yellowcake or something.) Or to build a base, whose goal it is to build a base, that can then duplicate itself without the first base. Once you have that tech stack, you'd have a pretty good idea what you need to do to start building self-sustaining space presence.
The problem is, it's intrinsically impossible for such a base to compete economically on Earth with the other entities using the local abundance of resources. It has to be a deliberate project.
If I were a billionaire targeting human survivability in the long term, this is actually what I'd be doing right now, not reaching for Mars. Once you have this in hand, you'd have something you could actually send to Mars and have some hope of it surviving.
(This gets you a good 80%+ of the way to super-long-term sustainability on its own terms; anything short of an extra-large planetary impact event would in principle be survivable by such a facility. Lifting it into space later would almost just be the icing on the cake.)
Breaking free of gravity, moving industry
Beyond the planet's surface into space
Lunar mines and factories, Lagrange Point colonies
Total productivity and nothing goes to waste
Solar-sailing ships deployed to mine the asteroids
While Earth becomes a paradise, her ugly scars erased
