Once u cash out can just move to Russia or another friendly country and never pay tax. Otherwise tax bracket for "conversions" or "distributions" will be only higher than if u do roth conversion today
If I keep putting $ into 401k and try to do roth conversions even at 50 and even over a 10 year period I'll be paying the same tax bracket as now , likely higher because taxes go up. The only play with 401k is take the $ and leave the country like tt.