That’s a useful article, and as impressive as these demos are, and how smooth Maplibre is, I dearly wish people would spend more time on building map tech that is actually based on geoscience.

The heat map is a good example. What does it mean? Points per what? And I can’t bear to talk about the tyranny of Web Mercator.

Maps are so much more powerful when they mean something, and convey scientific facts or actionable evidence.

As far as I know there isn’t a permissively licensed, open source map renderer SDK that can work in a true GIS, e.g. supporting multiple projections.

OpenLayers is probably what you're looking for. It supports multiple projections. It's a wonderful library, but a bit more ceremony is required than MapLibre/box and leaflet.