since that is approximately 127 years away, can we assume that the bitcoin supply will be inflationary for the entire lifetime of anyone alive today?
Doesn't matter much. Bitcoin is already deflationary in the sense that their price is rising.
The reason is that, while the money supply inflates, demand inflates even more. There is inflation, but there is no effective inflation. The price behaves deflationary, unlike that of the dollar or the euro, which is truly inflationary.