Much has changed since the SNP first fleshed out, in August 2006, its plans for a Scottish Futures Trust. The trust, as originally envisaged, was to become a more cost- effective and publicly-accountable financing engine for what Alex Salmond, at the time, called a "new age of improvement" in the delivery of public infrastructure projects across Scotland.

Like our Victorian forebears - favoured role models for the man who is now our First Minister - we would rebuild Scotland for the common good and save up to £116m a year in the process. Instead of "credit-card level debt repayments" under PFI, these savings would be ploughed back into even bigger public procurement programmes.

The "folly" of the Tory/Labour Private Finance Initiative (PFI) would end. More public infrastructure would be financed by public bond issues, like those used by American states. Assets would be held "in trust for the nation all without the unnecessary private profit that is an integral part of PFI".

It was all good resonant stuff, designed to appeal to an instinctive and widely-held Scottish mistrust of anyone making money out of the public realm. That 2006 document makes one fleeting reference to private profit being "a good thing".

But that token was quickly drowned out by all the tub-thumping about sky-high peripheral costs, for things such as parking and use of telephones, being paid for by patients in PFI hospitals.

How times change. Now in power, the SNP minority government has just told us how it plans to proceed with its futures trust pledge. And the picture which emerges from its consultation paper bears little ressemblance to what was proposed 16 months earlier. There is even an acknowledgement that PFI projects have "meant a significant addition to the provision of public service facilities over the past 15 years", raising capital investment in Scotland by, on average, upwards of £300m a year over the period. And a warm welcome for "the involvement of the private sector in infrastructure investment".

The "mixed economy" of delivery mechanisms used by the previous administration "has inevitably run on", we are told. And when the SNP Government gets round to creating its Scottish Futures Trust, it won't be prevented from making profits. It will just be prevented from distributing any profits it makes. It won't even be rooted in the public realm. It will be a body "which is private-sector classified but which has a public-sector ethos".

So why these profound changes? In its own words, in para 7.2 of the consultation, the new government is being "pragmatic". Under the current devolution settlement it has no borrowing powers of its own. Nor does it have the fiscal power to exempt from tax any returns from its proposed public bond issues. Such bonds are never going to fly this side of much greater fiscal autonomy or full independence.

For now a Scottish Futures Trust will have to settle for raising all its finance from commerical banks and other private investors. And because EU member states will sign up next year to new international financial reporting standards, which makes it harder to keep PFI-style funding of public infrastructure off government balance sheets, the Salmond government has decided its trust will have to sit in the private sector, where it can also, we are told, "harness commercial know-how and disciplines".

So what is it? A renaissance of the civic vision of 50 or 100 years ago, as Alex Salmond first had us believe? Or PFI-lite, paying private lenders their expected return, even allowing the trust to run up some surpluses on its own behalf, but just not distributing them to its stakeholders? Perhaps the new government is simply facing up to some uncomfortable modern-day realities.

The subtle mention throughout the consultation document of the unacceptability of "standard PFI" models of financing rather implies that non-standard PFI approaches are still on the table.

One massive change since the 2006 trust blueprint was published is the sheer cost of building anything of scale, like a new road crossing of the River Forth, in today's environment. In its original trust plans, the SNP estimated the capital cost of a new Forth bridge at just £600m.

Now, 16 months on, Transport Scotland estimates the cost of the SNP Government's preferred cable-stayed option (in 2016 prices) at a whopping £3.2bn to £4.2bn.

At the top end of the cost range, that's a seven-fold increase in just over a year. So Cabinet Secretary John Swinney is right to acknowledge, from the outset, that investment on that scale for a planned opening in 2016, "will put a significant strain on other projects during this period". And that's before we factor in any lasting impact from the global credit crunch, which could leave all borrowing, even that by public authorities, more expensive than in the past.

Ministers know they can't procrastinate any longer on a new Forth crossing. They also know its soaraway price tag threatens to squeeze out other much-needed developments. And it all has to happen in a timeframe - this Holyrood parliament and the one after that - in which the SNP seeks to create the conditions for an affirmative vote on changing Scotland's relationship with the rest of the UK.

That's a very tough call. It has yet to say how the new Forth crossing is to be financed. The bold path would be to say: Funding it through our fledgling Scottish Futures Trust would mark a decisive break with past practice. But a trust shorn, at least over the next few years, of the capacity to raise tax-exempt bond funding from individuals and pension funds, and located in the private sector to bypass changing international financial reporting rules, would then be at the mercy of how much the banks and the hedge funds would lend it and on what terms.

It seems a high-risk opening gambit in what started off as a high-minded campaign to change the way public investment and procurement is done. Or perhaps we are all missing something. In para 7.3 the consultation paper says: "The scope for uncapped investor returns as in the standard PFI' model has been discontinued." But then it continues the sentence: " and will only be considered in rare circumstances where the risks involved in a project are exceptionally high."

The risks of the Forth crossing costing even more than the already rapidly rising initial estimates must be exceptionally high. So is the prospect of it squeezing out other projects.

Might it end up as another standard PFI project? I wouldn't, at this stage, bet against it.