Thanks for the use case (now documented in our requirements system). As for the ability to use X command, it's not a permanent removal from Studio. Studio 5.1 (which runs on SAS Viya) is a subset of Studio 3.x (running on 9.4) and the plan is for 5.x to get to replacement value of 3.x before we can release it on 9.4 (kind of confusing, I know, to have a higher release number with fewer functions). The goal is to have X command (and the rest) available and controllable by an administrator. We just don't yet have the microservices support in the 5.x world to implement it.
For being able to switch back and forth between languages, one option is to look at the interfaces like SAS Enterprise Miner in 9.4 or Model Studio in Viya. I'm not an expert on either, but I think they both support models in several languages in the same flow.
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