Retail and Classic with a single profile: possible?

I've been boxing on Classic for a while, but I'm about to start boxing on Retail again for 9.0. This profile has only ever been used for Classic so far, but I'd like for it to support my Retail gameplay too.

My initial thinking was : since I've used virtualized class/spec keymaps, macroed most of the abilities, used ATGs for things like interrupt and CC, it should be at least possible to use just 1 profile for both.
But the more I think about it, maybe it's not so simple. The abilities of most classes are way different from Classic to Retail. Or at least different enough for a DPS rotation macro to be vastly different. I could see this requiring a lot of duplicated keymaps/hotkeys/macros, with just slight modifications -- leading to a cluttered mess of a profile.

So I'm curious: Is this even a good idea? Does anybody else do it? Is there a best practice for how to approach this? Or pitfalls to avoid?

I've considered the simplest solution: to just make a copy of the Classic profile, and let them evolve separately. But then if I make any major changes to one, it might be hard to merge them into the other.
Is there something better?

Thanks for your help!

[Wizeowel]

If you've already got a virtual key map that you are happy with, then retail characters are just extra 'specs' really.

Most dps rotations and macros will be wildly different, but I am guessing for the reset like drinking and buffing and mounting and interrupting there is more in common than there is divergent.

If you don't want an extra set of class key maps, you might consider adding ATGs 'classic' and 'retail', so that you can combine the key maps of each class.

For example In a DPS step for marksmanship you might have
action 1. /castsequence reset=target serpent sting, null -> self&classic
action 2. /cast aimed shot -> self
action 3. /cast steady shot -> self&retail

But I think personally I would separate classic and retail key maps, because it might quickly become unreadable.