I believe the total supply will not exceed 500 million full units in DNotes. Without doing any calculations (DNotes decreases I believe by 10% in block reward yearly), I'd take a wild stab at ~200 million DNote supply in 10 years.

Currently ~30k DNotes enter supply per day, which is just upwards of 11 million new units per year. This decreases by some 10% yearly, and there is 105 million already in the current supply. My best guess would be ~ 190-200 million DNotes supply by 2025.