I can't see why this would be good for Bitcoin. People said that it's good because it forces merchants to keep their stocks low, or produce goods only on-demand. But then you're asking merchants to change the way they have been doing business for decades, which seems unlikely to happen.
So how can Bitcoin solve this problem for merchants?
Lets take a scenario where annual deflation is 5% and you take 5% cut of each car sold. You have BTC100. First month you buy BTC100 car and sell a month later. Car costs now BTC99.5 due to the deflation. To take your cut you sell it for BTC104.5.
(BTC100- 5% / 12months)* 1.05 = BTC104.5
Pocket the BTC4.5 and buy another BTC100 car. Do that for 1 year and you end up with BTC154. If you count in the deflation you are now 58% richer.
If you didn't do anything then you are only 2% richer.
That is a terrible example: Your whole premise means that anyone doing business needs to KNOW THE FUTURE. You assume it will be 5% per year... with the volatility of bitcoin can be upwards of 50% or more.
How can you possibly set realistic profit margins when value can swing in such huge unpredictable fashions?