Regarding some ideas of how to determine the utility of a project to be funded, Luke has always been primarily concerned with CO2 emission, so one of the objective benefits/harms could relate to projected change in net carbon emissions versus realized change in net carbon emissions.
Ultimately though, in our vision of something like a Global Public Interest Bank, the objective measures of relevant benefits or harms to be factored into the credit equation would be up to the issuing financial institution and their board. It could be changing over time, much like central banks normally make adjustments, only for different reasons to achieve different ends.
As for an algorithmic application of this versus something like taxes, carbon tax is actually the main regulatory instrument that Luke has been championing so far, so this doesn't necessarily have to be exclusive with taxes, but an adaptive algorithm could have benefits over taxation.
Taxation is a bit of a crude instrument, while an algorithmic cryptocurrency can reflect what's going on in real time. If the implementation is flawed, this could also be its unique downside (you don't want the algorithm to spiral into insanity by doing millions of transactions or adaptations per second), but within reasonable parameters, a harm could be punished as it is happening, or a benefit rewarded immediately.
As for examples of benefits/harms that could be addressed algorithmically, apart from CO2 emissions, anything that can be quantified and measured could be factored into the credit parameters - number of people lifted from poverty or being provided whatever goods or services to which they were previously lacking access; the financial value of externalities remedied (like cumulative pollution decreased through cleaner or more efficient technological innovation brought to market) or environmental damage cleaned up; the economic value of lives saved by eliminating a disease, and so on.
The possibilities are endless, but any institution or society that's issuing the karmic credit should be eminently capable of choosing its priorities - what better future means according to it. "Public interest" is the key word here. as that's what’s being effectively invested into, counting real economy-wide gains as return on investment.