Or is it that there is a plan to obfuscate all internals at some point?
This could well happen, and it could mean whatever internals you are accessing become permanently unavailable.
A long-standing problem with JavaScript is it has typically had poor encapsulation: external code can easily mess with the internals of APIs. With newer features like private fields there is proper encapsulation support that makes it genuinely impossible for external callers to mess with internals. As encapsulation is a basic principle of software engineering and important for the long-term reliability of a platform and codebase, I would definitely like to use that throughout our codebase. This would however make all sorts of internals permanently inaccessible - much like they already are with any other game engine with any other technology that properly supports encapsulation, so bringing us in to line with the industry standard. This could permanently break engine hacks with no workaround. This is exactly why we have this warning, and why whenever possible I advise against it, since as per our policy we will not help anyone in this situation if they were using undocumented internals.