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Unity backtracks, no runtime fee for sub $1mil or for games on current/old versions
(blog.unity.com)
This is a most excellent place for technology news and articles.
Have you explored what level of effort it would take for you to convert it to use another engine? There are a TON of tools people are making to assist with porting projects from Unity to any number of other engines. Sure, the tools won’t do 100% of the work, but by what I’ve been hearing, they take a HUGE amount of the tedium out of the process.