Your best bet is to work with an existing open source CAD system, such as BRL-CAD, that includes support for numerous importers and exporters.
Your intuition that learning a given format would be difficult to understand and implement support for is quite true, particularly when dealing with solid geometry formats intended for analysis purposes. Preserving solidity with topological guarantees is important for producing valid analyses, but rarely addressed by simple mesh formats.
In particular for the two prevalent international standards (IGES and STEP), they are excessively complex to support as they can contain the same solid geometry encoded in numerous ways. Consider a simple sphere example. That sphere could be encoded as a simple point and radius (with no explicit surface information, an implicit form common with CSG usage), it could be a polygonal mesh (lossy BREP facets mesh format), it could be a spline surface (BREP NURBS), it could be volumetric (think CT scan data), and more. Focusing on any one of those involves various tradeoffs (simplicity, solidity, analytic guarantees, flexibility, etc).
As mentioned regarding BRL-CAD, it's a large open source solid modeling system that has a lot of functionality in many areas you could leverage, about a dozen libraries of functionality and more than 400 succinct tools (two dozen or so being geometry converters). Even if it doesn't do exactly what you need, you have the source code and can contribute improvements back and collaborate with an existing community to help implement what you need.