What if a 9-9-9 tax code is ever adopted?

I’m sorry if this question has been raised. Surely it has but I could not find it.

Without getting into the probability of a major tax code overhaul (ala the espoused 9-9-9 plan) actually occurring, should a person who is considering a sizable Roth conversion be concerned about the effects of such an overhaul? My tax rate, without conversions, is about 10% each year. I have been Roth converting an amount each year up to where my marginal tax rate hits 25%. This puts my overall tax rate at about 16%.

If some form of flat tax such as the proposed 9-9-9 plan were imposed, I might want to reduce the amount of my Roth conversions. Why would I pay 16% now when I can wait and pay 9% later?

Please refer me to the thread if this has already been raised. Many thanks!