I've placed Seaside2.8a1-wbk.523 on to the Seaside SqueakSource repository. This is a patch that moves the serialisation of contexts from Continuation into ContextPart. This is to allow Seaside to work with Exupery.
Is it possible to get this merged into the development branch of Seaside?
Yes, the latest development versions of Exupery will run Seaside, no, it's not yet practical. Expect bugs and don't expect a performance improvement yet.
Bryce