This was just covered.

It has also been covered countless times on countless threads. It breaks down like this:

1. Yes it's DOABLE.
2. There is a difference between the keyboard rotating, and any other app rotating. That difference is that the keyboard is programmed TO auto-rotate. Conversations is programmed to not auto-rotate (it's programmed to be rotate-able, but it doesn't turn on set to auto-rotate, so another program has to set it.)
3. But realsportscars doesn't want to do that as part of his vkb, because his keyboard is just that - a keyboard.
4. Why can't we just reprogram Conversations? Because the source is closed, which means you either start editing/disassembling/whatever the binaries, or you clone Conversations completely. (THe former is of dubious legality, the latter would be difficult to pull off to say the least. I'm sure it'll get done eventually, though.)

So yeah. I myself suggested a page or so ago how you can do it. DBus scripts + wait until a Conversations-has-been-launched call over DBus + send the same call that Shortcutd sends when it enables rotation. (Which you can look at Shortcutd source code for.)