Ignoring possible implementation difficulties, the application of a repeated oneof seems very esoteric. In most cases repeating the underlying fields is cleaner then repeating a oneof. E.g. instead of

    repeated oneof Option {
      Foo foo = 1;
      Bar bar = 2;
    }

use simply:

    repeated Foo foo = 1;
    repeated Bar bar = 2;

There is no longer "one of", therr are multiple, so why keep the complexity? If the interleaved ordering really matters, you can always fall back to a sub-message.