These already have a name:
創作寿司
Sōsaku sushi
(Translated as "creative sushi")
So long as nobody is trying to foist any of these concoctions on me whilst declaring them to be authentic Edo style sushi, I'm fine with them as examples of sōsaku sushi or poor man's sushi.
There's a wonderful scene in Ruokala Lokki/かもめ食堂/Kamome shokudō/Seagull diner where some Japanese friends and a young Finnish man try out alternative, local, fillings for onigiri (reindeer, crayfish & herring). They don't proceed.
Here's an example of sōsaku sushi that was made in China, the
Japanese diner who ate it doesn't exactly recommend it...
