If they ape the Windows 8 snap view completely, it won't work in portrait.
It will be interesting how they deal with installing phone apps on the tablet. They might just allow carte blanche or might require a developer to opt in to avoid issues with phone specific apps being unusable on the tablet.
What issues would they have with phone-specific apps, other than possibly lacking a microphone and cell plan? If their security model makes the developer list what sensitive APIs (like voice and location) they use, then they already have enough information to disable apps that depend on having a microphone.
If you mean having apps work on bigger screens, it looks like side stage lets them keep phone apps at a reasonable phone size. They might require opt-in to make phone apps fullscreen - that seems reasonable. (Although it sounds like one of their goals with QML is to make it easy to write apps that grow with screen size, so they're hoping that almost all apps will be able to do it.)
With Skype around, I'd imagine that microphones are actually pretty standard on tablets nowadays? And it's not terribly uncommon to see tablets with HPSA+ connections (or even LTE), right? Tablets and phones are rapidly becoming one in the same, just with different screen sizes.
It will be interesting how they deal with installing phone apps on the tablet. They might just allow carte blanche or might require a developer to opt in to avoid issues with phone specific apps being unusable on the tablet.