it applies as the topic is about improvements L will bring, and that being a feature i think would BE an improvement.
i know about launchers, and i know it doesnt inherently do it. unless you have it docked. at least, the motorola versions rotate when docked for the "car" or "desk" mode from what i remember of my old razr
And I don't think it would be an improvement at all. This thread doesn't really exist to discuss fantasy features; I think Google brought enough to the table that discussing what is actually coming ought to be plenty. Like you said, "improvements L will bring," not "things I think are improvements that L should bring."
I would further argue that homescreen orientation is not such a hard to implement feature that Google itself has to do it for it be done right. Dashclock is great, but Android just putting notifications on the lock screen is better in that it doesn't require the app to support yet another API. Homescreen orientation is easily enough implemented in a third party launcher without seeming hacky or over-burdening app devs.
There's a line for features that should be done by Google, and features best left to devs. I don't think homescreen orientation on phones falls into Google's lap at all.
Granted, if they want the GNL to be more competitive, things like icon themes, more freedom in widget re-sizing, grid size and homescreen orientation are things they'd have to bring. But that's still not an Android feature. Android doesn't have to change to allow that.