Vanguard has a non-profit foundational division that manages this for an org: https://institutional.vanguard.com/VGApp/iip/site/institutio... There is no need for Watsi to handle the management of these investments/funds.

> Wouldn't it fundamentally change the company from a small, lean, product-driven global health nonprofit to a socially responsible investment (SRI) company (which there already are many of)?

Nothing would change except Watsi having more consistent funding and the ability to have a longer term strategy.