I’m not totally clear what’s meant by “social impact” business or “impact metrics”. Many startups build an element of positive impact into their overall business model but don’t necessarily define themselves as a “social impact” business, so I would hesitate before saying that there is a separate set of metrics investors would expect to see. Ultimately, if you are pitching to an investor rather than a philanthropist, you are still going to be judged as a commercial business and the potential return you can deliver on their investment.
Speaking more generally of early stage metrics to consider: as with any business, it is important to outline the specific problem you’re solving and prove there is sizeable appetite for solution. Any metric that demonstrates consumer demand for your product is important.
If you are describing companies in climate tech or sustainability, I would say it’s a great time to build. For a host of reasons, corporations need to commit capital to affirm sustainability credentials, which has created a viable business opportunity for startups to play in the space across multiple sub-sectors.