You could put breathing room in by setting a high difficulty growth target (I thought 50% per annum was high, since it implies a 125% increase in computational speed every two years). As I understand Moore's law it is a 100% increase in computational speed every two years.
If you want an inflationary currency, why all the complicated stuff, and not simply set a fixed inflation rate of, say, 2% per year instead of the current 50 coins per 10 minutes? And remove the cap at 21,000,000. The only thing that would be needed is to base miner payouts on the current total number of coins (which is trivial) and you have your geometric "growth".