Ok, my N900 didn't crash, but I have bad news.

Jessie's libc6 (the single most important package - even more important than the kernel) needs a kernel version >= 2.6.32. There is a check for the kernel version in the preinst script of the libc6 package. I adjusted that check to match Maemo's 2.6.28 but libc6 still insists on wanting at least kernel 2.6.32.

So I had a look at the libc6 sources and it seems that the package will depend at least on whatever kernel version was installed on the system it was compiled on. Since Squeeze had kernel 2.6.32 this kernel version as a libc6 dependency makes sense.

So in theory recompiling libc in a Wheezy ED image should fix this, but unfortunately Jessie's libc6 sources depend on a g++-4.7 version that is newer than the one in Wheezy and Jessie's g++-4.7 depends on a libc6 that is newer than the one in Wheezy.
So the vicious circle is complete.

I stil have hopes this dependency ring can be circumvented somehow, but as it stands now ED won't be dist-upgradeable beyond Wheezy.