Given the power of Openlayers + JSTS I'm a bit surprised nobody has built a general purpose WebGIS app. QGIS is often too heavy or inaccessible. And I believe that GIS is something everyone can do. You don't need a fancy degree and training to explore spatial data and build maps. I tried once but quickly realised it was beyond the scope of a part time project.
I built an extensive open-source Rust-based spatial analysis platform called WhiteboxTools with the intention of serving as a plugable spatial analysis back-end for various GIS front-ends. So far people have created front ends for it in QGIS, ArcGIS, Python, and R, but I have long wanted to see people use it more in web-GIS. Perhaps one day...