So I wrote today to Kees Joosse from TSMC[1] and asked him whether they would accept an order from us sending them just the GDS2 files generated with the openly available design rules here[2]. I'll tell you IF I ever hear back from him... haha
[1] https://www.linkedin.com/in/keesjoosse [2] https://git.libresilicon.com/?p=redmine/qtflow.git;a=blob_plain;f=tech/osu01...