The counter argument is that bitcoin devs/investors might not WANT the new feature that makes Bitcoin2 special, or regulators and lawmakers may exert a lot of pressure to not include it.

For example, look at zerocoin.  Supposedly they are going to launch an alt-coin that will offer real anonymity.  The bitcoin community seems to be a house divided as to whether that is desirable or not.

So maybe we end up with bitcoin that is trackable, and zerocoin that is not.  Both are valuable and have their uses.

I could see them co-existing for quite a while, though I do tend to think that a majority of people will opt for greatest fungibility in the long run.