I really like using multilines but miss the opportunity to fill them automatically with hatching or adding transparency to the filling colour. It would also be ideal to be able to put the filling on a layer of its own, too. Maybe it's also an option to fill certain areas of multilines. All of this would make multilines a way more powerful tool as it already is.
I doubt Bentley will look at improving multilines. I can't remember the last time anything was added to mlines. Decades
We will look at including this as a future consideration for MicroStation.