I think these inflation questions highlight how risky it is to make 30-40 projections when analyzing the finance of DVC. These calculations are all based on estimates. For some estimates, "close enough is good enough." But interest rates are tricky if you are going to compound them over 30+ years.
When looking at any sort of financial decision, I'm much happier looking at no more than 10 years. If I can show that DVC makes financial sense over a 10-year horizon (and for me, I can) then any benefit from years 11+ is just gravy. But if takes more than 10 years for things to make financial sense, that's too risky for me (for me - I'm extremely fiscally conservative.)