There were proposals for mechanism for extending types from several of Wirth's students, and Franz - one of the co-authors of Juice - was one of the people who around that time wrote a report on a proposal that'd enable runtime-loadable interface-based extension, so all of this would certainly be fixable.

Juice also flows naturally from Franz PhD thesis, which was on JIT compilation of Oberon from what in some sense was a compressed serialized reduced form of the AST instead of bytecode [I'll stress this is a gross oversimplification - his compiler does do more processing, so I guess what is serialized is closer to an IR in tree form than the AST]. I don't know how much that changed in Juice, as I've never looked at it much but from the description it remains at least similar in concept. I've wished more work had gone into that ever since I read his PhD thesis in '94.