minerva already beat me to this, but I would like to expand on my reason as to why I don't agree with your statement.

First, 'X' can be thought of as variable, whereas in my suggestion it is not, but instead a statically increasing rate for all time (ignoring an initial growth period which is essential to any new system like this).

Second, I believe that a static supply has the potential to increase price VOLATILITY, since the quantity of the currency would slowly decrease over time (see premise #2) thereby driving up prices.

Please don't mistake my ideas to suggest that we could have perfect stability.  I only seek to determine if offsetting the loss of currency by steady inflation would help decrease the volatility of prices as compared to either fiat currency (where inflation is unchecked) and a system with a static money supply (where deflation would be unchecked).

In any case thank you for your post, it helped me being these points (previously omitted) out.