Non-profit community financial institutions are credit unions. They’re generally disappearing though, in many segments, especially as regulators force organisations to merge for ‘scale’ to pretend like they need to compete on scale with big banks.

Loans can have cosigners. There’s generally a limit on that based on logistics. Theoretically you could incorporate a business, and take out business loans, with convoluted payment schemes like you’ve indicated for users of that business, but such things are generally not approved by FIs due to the high risk of default on such things. Crowdsourced projects already have a very “I sent the money, maybe one day they’ll deliver star citizen” type feel to them. Imagine trying to balance that risk, against the interest amounts you need to pay on deposits… it’s practically a non starter.

Another issue is that interest gets paid to the bank, and the bank pays interest on deposits, on a routine/regular basis. Trying to shif the payouts overtly into a scheme where its a lump sum after a long duration, introduces even more risk to it all. Like mortgages typically have something like an 80% LTV minimum (loan to value of security), so that if the borrower defaults in the first year, the bank can still foreclose and maintain the interest payment commitments to depositors. If you didn’t have to pay that depositor their interest for 25 years based on the agreement, you’d pretty much guarantee that the organisation fails to make its financial commitments to the depositors.

Put slightly differently, Credit Unions are already “crowd sourced” mortgage options with established repayment functions for the depositors, which follows a more stable and lower risk approach – but their “crowd” is just their memberbase (which has generally been declining for decades, as people don’t care about this sort of thing in general). When you “buy”/lock in a deposit, something like a $5000 term deposit for 5 years at 3% per year interest, that money basically gets combined with a bunch of other peoples term deposits, and used to provide a loan to someone in the community wanting to get a home. That person then commits to a 4-5% interest mortgage, where their interest payments cover the operating costs of the organisation, plus the deposit payout to the depositor with the term deposit. If the borrower can’t make payments, the CU can foreclose on the property and continue to make the 3% annual interest payment on the term deposit – so your deposit is pretty much assured, and is very low risk compared to other savings options. Stocks yield higher returns, but involve much more risk – s’why people aim to diversify portfolios once they get to a point where they can save a bit.

And as a side note: most times you hear complaints about savings / deposit interest from a bank/CU, it’s because the person just has their money sitting in a demand account like a chequing account, or a chequable savings account. You gotta lock it in to a term/gic or something for it to get an interest rate that matters – and CUs/Banks pay out on those more, because they can do exactly what I described above with those funds… while if the funds remain available to you ‘on demand’, it’s arguably useless.