A 2D solver works great for sketches and some kinds of assemblies. However, it is insufficient for many kinds of 3D assemblies. The solver Ondsel released (LGPL) which underlies the new integrated assembly workbench is a true 3D solver.
https://github.com/Ondsel-Development/OndselSolver
Correct. Variable sets (varsets) is partially merged into upstream main development branch. Other work is ongoing. Varsets are much more important than just our web service though. Being able to configure and control variants in a design is underappreciated and will be essential to having complex assemblies with multiple copies of identical parts. Imagine a hinge that is reused in many places in the design. The current angle of the hinge should be controlled on a per-copy basis. When you change the angle, you don't want all copies everywhere to reflect the new state. This is a variant.
We're an open-core company building commercially around FreeCAD. We're leading the development of the new integrated assembly workbench and contributing to many parts of the application. We have our own build of FreeCAD which includes our latest contributions.
We're also building an optional web-based file sharing and collaboration layer.
It's great to see others investing time and talent into open-source CAD. At Ondsel, we believe open-source CAD is incredibly important and we're thrilled to see innovation in this area.