Nice idea, but would require changing some laws.

In transportation planning, you have a 20-year plan and a 5-year funding program that implements the upcoming parts of the plan. But even the funding program rarely provides for complete project funding in one go unless its a pretty small job; it gets split into phases that are individually funded as their time comes ... if the money is there. If the money gets yanked, the project is delayed, and if it's a big multi-construction-phase project you pretty much have to expect pauses in funding as time goes on. No politician is going to commit to a "framework" that limits their ability to change funding priorities at whim.

Then there are the spending laws: in general, the funds are appropriated and must be obligated within one fiscal year. They must be spent (in California at least, which is similar to Federal law) during the year of appropriation and the following TWO. Not 20, not 50, TWO. With legislative and administrative approval, a contract that doesn't require additional funding can be extended, usually, by no more than one year beyond the original 3. Funds not spent by the end are permanently lost, reverting back to the fund source. So again, there are hard legal limits on individual expenditure packages that guarantee pauses in funding unless there's really firm political buy-in to annual fund infusions.

HSR, whether or not the polls are correct about public opinion in favor, does not have the political buy-in required to maintain a steady flow of funds. Some "framework" will not change that. So it's a nice idea, but it needs a little more cooking.

Really, it's always been that way. Past megaprojects like the big aqueducts took 5-10 or more years to build (even before CEQA!), and rarely had full funding up front. Life just doesn't work like that. The truthful ones told the public that they needed bonds for $X to start the project, and would be back for more, perhaps more than once, as construction proceeded and new issues came up. Hetch Hetchy was an example. There can certainly be an administrative framework for maintaining some kind of project continuity.

But the public can't be outright lied to: they need to be told up front that the final cost can't be certain, except that it'll certainly be more than anybody can expect up front, when you're doing a one-off or the first of its type in the region. HSR did lie to people about both the likely (though not certain) cost and has continued to mess up and cover up, which doesn't leave even its supporters with much good feeling. A "framework" would be great, but has to be realistic even if not precise.

Also, helps to design the framework so things can be built in individually useful chunks that can synergize as a whole. HSR reacted to fleeting funding blocks to do things in the most wasteful way possible, ignoring potential interim connections and uses, and it will probably take at least 10 years to recover from that and make progress toward a useful (not just Minimum Viable Product) system. They are not *entirely* to blame for that, due to highly political funding drops and clawbacks, but are only recently at least talking like they know what they're doing. Might be too late. Kopp and friends included a few poison pills in The Proposition, too, that haven't helped matters.

At least they got Caltrain electrified, and it's working as desired (i.e. better, and with higher ridership). Now if only they could get a consistent operating funding scheme - they built it, the riders came, but now they don't have the money to keep running it (on the plus side, the power costs less than burning diesel did, so the end can be postponed a bit). Same with BART and others. And it will be the same with HSR if it ever gets beyond the test track stage: I think more people will use it than anybody expects, but it'll take 20-30 years to achieve an operating profit once most of the line is working (typical of other HSR lines in the world) and that's just politically unacceptable in an instant-gratification society (political and otherwise).