Calls between layers should be WCF service calls

Everyone knows about creating layers in software architecture.  During the IDesign Architecture Clinic I attended in March Juval talked about separation of layers and stopping leaking of concerns between layers.

The best way to achieve this is by using WCF between layers.  When this is applied correctly WCF will provide:

Consistency between layers (transactions);

Scalability (general code performance, farming, or partitioning layers onto different app-servers etc);

Fault isolation (resilience from unhandled exceptions and isolate each thread from another's exceptions);

Security (message encryption, transport encryption, authentication, impersonation etc);

Clean Separation of presentation from business logic (maintainability and flexibility);

Availability (striving for 24/7 99.99% up time);

Responsiveness;

Throughput;

and Synchronisation.

Juval Lowy: "Tell me which one of these you don't like and I'll tell you in which way your system is going to die." (reference)

Juval is also known for saying "...every class as a service...". This might be a little controversial and extreme, but imagine for a moment that the cost of serialisation and deserialisation was eliminated for internal App-Domain calls.  Why would you not want all the above aspects WCF brings to the table not only between layers but also between classes?  An insight into the future perhaps?