Why don't you do 3-5 years? Thankfully you give yourself 730 days clearance. Good show mate. Why I stand by no one has a clue. May as well do 5 - 10 years too.
5 to 10 years would be a clue. 3 to 5 years would be a clue. No clue equals - no one anywhere has any idea how long we have after FDA final rule is put into effect.
Another indication of no clue would, for me, be to state that once the deeming is finalized, all products will be removed from the market within a matter of a few days. But if someone provided reasons to support this, then that would indicate they do have a clue.
The 2 to 4 years scenario is the opposite of that and is asserting one of 2 primary reasons why the 2 to 4 years make sense. Because government moves very slow on such things. If look at original proposal from April 2013, it was stated that sometime in 2013 the final rule would come out. Why would anyone doubt that? Other than previous experience with government where they may put forth wording that says "this will happen on specific date" and a couple years later is when it actually happened. But if for some reason that doesn't fit in with your understanding of the issue, then the FDA deeming does state a compliance period or grace period to take existing products and allow them to be approved by FDA. Now, that could change and with state laws, could be significantly reduced. But if still on shelves in say Idaho, West Virginia and 18 other states, while 30 other (blue) states are operating under guidance of "off with their head," then it would still be on shelves and product could still be, rather easily obtained (even in a state where shelves are all clear). But all of this assumes no political fight nor any legal fight is occurring. If FDA were to lose any legal fight, and for sure if they lost a political fight, then 2 to 4 years would be on the low end.
The only antithesis to what I'm saying with 2 to 4 years that I can think of as reasonably occurring is I think right now there are vendors that are getting cold feet and planning on leaving the market shortly after FDA ruling, realizing that (for them) the lucrative market will be dead. So, they may choose to go out while still ahead. I can see that happening with a number of companies within first month of final rule. But even under that scenario, their product wouldn't be removed from shelves, but more like once their inventory is out, they won't be resupplying anyone with more product.