Well if you want to play with ipv6 then you will have to move to 2.1 - if your setup is generic then just do clean.
Maybe I am spoiled with running mine on vm, but it takes takes no time at all to try this version of that version - if need be roll back, or just switch to different vm running different version, etc. Every now and then if someone has issue with older version I want to try and duplicate I just fire up a vm with that version on it, etc.
So maybe I am spoiled with time to spend - since there isn't any really, only takes minutes to switch around what distro I use for my router - be it pfsense, ipcop, m0n0wall, etc. Since I can have the VM use the same mac as its wan don't even need to restart my cable modem.