Absolutely bytecode was already an old idea by the time this work took place. (And Wirth, Franz's advisor, wrote compilers and books using pcode).

The novelty was in using trees for the representation, and recompiling the entire Oberon system not just a single app. Later work by his students (Vivek+Chris iirc) looked at using arithmetic encoding to further compress things. Also Michael noticed that it prevented malformed programs, as his interest in security grew.

Another branch of the family tree worked on more compiler optimization friendly IRs, such as typed SSA instead of bytecode, and applied it to Java. The idea being to be able to do more upfront optimization work, and still transmit a safe representation that was cheap to verify.