Can you show where the 16th Amendment REQUIRES any of those things ? If not, then why would eliminating them be unconstitutional ?
No, not at all. It is all quite constitutional and nothing REQUIRES the 16th to be repealed first. In fact it would be virtually impossible to do so.
Having the FairTax as an operating tax law, though, would keep us from having both an income tax and a sales at the same time while the 16th is being repealed. In fact nothing right now keeps us fom having both at the same time and there has been at least one bill introduced to do just that.
There have been almost 100 years now during which the 16th could have been repealed, That should make it patently obvious to even the most die hard Status Quo Lover that the 16th won't be repealed until a completely different tax bill - one not relying on income tax - is in operation. That, of course, is exactly what the SQLers hope for ... that it won't be repealed but keep right on with more of the same old, same old.