Does the Measure M sales tax have no sunset? If so, in principle, you could revenue bond against tax receipts until Kingdom Come and build everything that's in anybody's transportation wet dreams right away. Maybe even the south end of HSR! But then there's operating expense, which by 2040 or so will need a large and growing chunk of those tax receipts, so the money actually really isn't there for a do-everything-now capital plan. Neither are the contractors, though that could be adjusted with enough extra money.

The published plan is pretty extensive, though obviously not including everything imaginable and scheduling a lot of things for well after many of us will be dead. That's life: a sales tax does not bring in infinite funding unless you do indeed look out forever. Even with a tax that has no sunset it's not good policy or financial planning to look more than 15-20 years out (with periodic updates, as with other formal plans like RTPs and General Plans) at a time. Too many things can change to make firm commitments to stuff that's way out there appropriate.