Since V5 is mostly about making it more mobile device friendly.
How about making V4 defualt and have a 'View On Mobile' button/link to switch to V5 for those that are viewing on a mobile device to hit?
We will absolutely be doing this.
Is it easy to allow the users to change to the version they prefer just for their own? So it will be like choosing a theme...
I love it. You definitely got my 3 votes for this one.