Btw, the other day Unity announced that the Steam integration for their Platform Toolkit was going to be a Pro-only feature.
It only took me a week to replicate the exact functionallity and publish it for free on GitHub: https://github.com/GerardGascon/Custom-Steam-Platform-Toolkit
I don't know if it is a 1-to-1 version to their implementation (as I don't have the money to buy a Pro subscription), but all the features publicly announced are already supported in case anyone also wants to avoid paying Unity Pro.
