that’s not true… STEP is the de-facto mechanical standard interchange format…
please have a look at the most commercial ECAD brands and you will see that STEP is the adopted standard for ECAD/MCAD collaboration.
Anyway KiCad supports both STEP and IDF… the only problem is that no one of the on-line resources are deploying an IDF library and the same for KiCad… IDF was supported since a while ago,before STEP came in with StepUp…
But very little were using this because of the lack in 3D library parts…
Please send these files
demo.step (947.3 KB)
https://raw.githubusercontent.com/FPGAwars/icezum/master/3D/icezum.step
to your SW experts and see if those are fine for them…
Both are exported from KiCad…
And here a board exportable in IDF with KiCad
You may do your considerations
PS in two and half years from the first StepUp exporter for KiCad this is the first request I knew for IDF format at this forum…