One does not know how valuable this service would be if society were not cash-poor and beholden to the rich for liquidity, but I think it still would be highly valuable. The trick is to separate the activity from the practice of over-rewarding the holders of capital, and it's no small trick.
As far as government lending goes, we are all borrowers from each other. Most of us "invest" through taxes and the profits we generate, but must all "invest" somehow and trust that, in time, our "investment" in society will reward us. It's true that government debt created the securities and financial market, but that hasn't been such a bad thing. It's better than having rich people's money sitting in vaults as gold coins, gathering dust. The power to tax - an expression of a citizen's financial obligation - allows the government to borrow at the best terms available to anyone. We charge ourselves very little interest and have the power to inflate away the benefit of that interest if we choose. I don't think it's too terrible that the government borrows from the taxpayers - it smooths things out. The real issue is that everyone government or the public has to borrow from rich people to create even the basic mechanisms of exchange. And the distribution of wealth shows that a dollar saves by a rich person earns *more* than a dollar saved by a worker. The advantage of being rich is self-perpetuating and increases with wealth.
To reward lending in some way is not insane, nor does it threaten to bankrupt the society. But the rich demand some sort of toll at every point of exchange. That's not "primitive" accumulation. That's a force that shapes society. Every part of our society must reward the rich (at some level) or eventually it will very likely either not get funded or find itself out-competed by some similar good or service which does reward the rich.
But primitive accumulation long ago ceased to be our problem, if it ever was. In fact, I think that there is very little history to suggest that there has ever BEEN primitive accumulation - unless you count stealing. Remember that the first purpose of government borrowing was to fund wars so that the powerful of one society could steal the assets of the powerful of another society. The better-financed society (which became synonymous with the more-broadly financed society) generally won. And the powerful have, as far as I know, always controlled the financial system, so the system the rich have access to today was created by and for an elite.
I think Marxists and Friends worry entirely too much about primitive accumulation.