D didn't say unfeasible, just that AM advised against it. One good thing about having macro algae in a tank is that it uses the plant food, namely phosphates and nitrates, that niusance algae would use to grow giving you less "ugly" algae blooms. It would serve the same function as having a refugium, it's just in the main tank.
There are plenty of kinds of macro algae that are relatively slow growing that I'm sure would make good candidates. In my opinion Animal's tank looks awesome with the macro in it. While playing with the octo if you pruned a bit every day or two I'm sure it wouldn't be too much of a burden if that's the look you're going for.