It may be that we are talking about two different things when we talk about transitional difficulties. I think you're speaking of the administrative apparatus to collect the tax. I too don't really see any issues there.
When I speak of transitional issues, I'm speaking of the effects on the economy and employment during the four to six months prior to and a couple of years following the change over. Any change as fundamental as this change will have unforseen impacts. Regardless of the merits of this proposal these risks are there.
I think there are far fewer risks economically than you apparently. In adition as pointed out by #1337 the REAL risk is continuing speeding down the dead-end alley where we now are.
Think about what p_w displays so clearly in that post. It is clear that the Tax Panel is going to recommend something to change the present system and I think those changes are likely to be far more that just tax code tinkering again.