In the context of the OW course you have to wear what the students are wearing. I'm not sure that rule is carved in stone in the standards but your job as an instructor is to assist your students in becoming familiar with THEIR gear... not yours!
If every gear related demo you do is then followed up by having to explain that the can't do it the way you do it then you're not teaching them, you're just being stubborn and putting them at a disadvan...
I wouldn't try to demo in different gear... that isn't a demo.
You are right about the standard. It isn't carved in stone so I called PADI before I did it. They have no problem with any gear configuration as long as it is safe.
For the CW I wore the same as they wore so demos weren't an issue. In OW I wore a long hose because it is popular in my area and I wanted them to be familiar with it. Other than a few minutes to explain what I was wearing and why, it was a non issue.
Demos were not an issue because I don't do those on OW dives.
As long as someone (DM) has the same gear to demo it would have also met standards in the pool. Also, having everyone in long hose from the beginning was an option but I'm not trying to change the world, just introduce students to something they may see.