SkunkyArt | Hideyoshi — Hardsurface

Export/import pipelines would need to change.

Custom tools need to be re-written or replaced.

Huge parts of the QA pipeline would need rework.

Any documentation, policies or work instructions referring to old tools need to be updated at best, re-written at worst.

Everyone who uses the software needs re-training.

Everyone who uses the software will drop in productivity for somewhere between 3 weeks and 3 months as they get familiar with the new stuff.

Software will have to be uninstalled and re-installed on most if not all workstations. (This will result in days or potentially weeks of cumulative downtime.)

All existing data saved in the old software's formats need to be converted to the new data's formats. This is a potentially lossy and/or destructive process, so needs its own QA process.

Everything that any of the art pipeline touched needs re-testing, and will almost certainly need maintenance work as a result.

There's an ongoing cost of training new people, as well. Students are usually trained in one of the big commercial packages, so re-skilling for Blender would be an overhead. On a closely related note, bringing in new people on short notice would be made far more difficult by using less common software.