One important thing even though a great deal of thirdparty sources are removed with the exception of 6S library (radiometry) and SIFT algorithm source. Indeed, these two sources can be excluded since OTB 5.0.0.
I raised this point, because last time there was a discussion on the copyright of 6S code. We had given permission to use 6S code but it lacks a proper OSI approved license. The original code is in fortran and we uses a modified version (translated to C code).
Is it be possible to get an exception for these sources?
However, easiest solution is to remove the sources and deactivate them during build (Radiometry and SIFT features will be disabled). If an exception is possible with some sort of procedure/validation/review that can run in background as OTB 5.0 get ready for Debian.