Question for Microsoft devs regarding Windows Phone development and possible changes with Apollo

There's rumour floating around that Windows Phone 8 "Apollo" will be adopting a large portion of the WinRT library and Windows 8 kernel. This seems to be logical, since no way would Ms not have their tablets run the same Metro Apps/code as on the phone and vice versa since otherwise that would be too much work for devs and thus fall behind competing OS's on the tablet and smartphone that already do this.

What I was wondering about though is considering there's some 70,000 apps in the Windows Phone marketplace now based on the current Silverlight/XNA derived framework would Windows Phone 8 have to be bloated and support the older framework mentioned above a long with the new WinRT based one in order to run all the existing Apps in the marketplace? I hope not and wish it's just a matter of the runtime providing namespace pointers/re-addressing to new classes for the existing Apps based on the current framework to their identical counterparts in WinRT, but none the less I would think a lot of classes that would otherwise not be needed will have to be baked into Windows Phone 8's WinRT implemetation to support existing apps.

I have a suspicion Windows Phone 8 is bout to get a lot more fatter.