Sometimes it’s easier to just answer than find a post. I think I discussed my reasoning somewhere in the Journey to JSR223 Python 1 of 9 or maybe in the Experimental Next-Gen Rules Engine Documentation 1 of : Introduction but didn’t want to scan through them to find. Some of those posts are old too and a lot has changed since posting.
As with anything, there might be quirks or odd differences. I’ve not encountered any but that doesn’t mean they are there. Zulu and OpenJDK are two implementation of Java and there are little differences in behavior and such between those too.
Think of it like differences between compiling with gcc verses xlc. They both compile C++ but there are differences.
All I can say for certain is that Rules DSL has been ported to and is available to run on the OH 3 Rules Engine (called the Next Gen Rules Engine, NGRE, Experimental Rules Engine, etc. in OH 2.). The current Rules DSL Rules Engine is gone but the language remains supported. For how long remains to be seen but I would expect the language to be supported for a good long time.
Rules DSL still has support in OH 3. But there will be subtle differences in how they run. I don’t know the extent of the differences yet.