I'm planning gold rims when the wheels need rebuilding, which is likely to be this year I reckon.
I'll stick to the 21' purely because the tyres are cheap and I know what works for me and the bike.
Back in the very early 00's I had a DR600 Djebel that I SuMo'd by lacing the old 17" rear rim to the front and a wider 17" on the rear.



The footpegs ended up half length due to scraping on bends and roundabouts but handling wise it was fine up to around 90, when the front would feel a bit flighty. Just had to keep a firm hand in.

I don't think 19" from 21" would render the bike hard to ride at all. Mine currently has +35mm jack up at the back and is fine.