Yes, I just topped up 500mL after 2500km, i.e. the amount it takes to go from dipstick half to dipstick full mark. I'll post an update after the entire interval is complete.
The engine is from 2006, which is supposed to be after the piston design was changed to mitigate oil consumption, but the ZZs are known for their oil consumption and crankshaft axial play issues. Interestingly, the original engine failed at ~150,000km because of oil pump failure that caused oil starvation related irreparable wear.
However, this engine runs fine, so I'm going to go towards a full syn A3/B4 5W-40 oil for the next oil change.
Right now I've topped the Aisin 5W-30 greenTech+ Full Synthetic oil with Caltex Delo Gold 15W-40. That's a calculated viscosity of 10.67 cSt @ 100C, with 11.9% Delo Gold. Even if I had a 50/50 mixture, I'd still be in the viscosity spec of a 30-weight oil.
Although, If I end up having to change all of the oil through attrition over its remaining service life, I'll just switch to a full syn 5W-40 and check consumption and seals. Otherwise, heavier 5W-40 or permanent 15W-40 HDEO.
I still don't think I would ever have a reason to use 20W-50, but you can see that the only reason would be a band-aid, i.e. it means something is wrong with the engine.