Emacs has finally gotten rid of unexec. It's replaced by the portable dumper which which essentially serialised the state of the application using its own format.
Assuming this issue is up to date - yes, but it's on the todo list to remove:
Wait, what's the reason for preventing a dumped and reloaded emacs from being re-dumped?
As linked, it's mostly incompatible with ASLR. If you were to undump to a different address, all the pointers break.
Why doesn't that affect the initial dump/unexec?
(Or in other words - if the answer is that ASLR is turned off for either initial exec or reexec, why not keep it turned off so that a third exec works?)
Oh, it does. Sorry, I missed the point about the double dump. No clue about that. I'm happy not knowing.
If I remember correctly, the same kind of hack is used by atom to allow fast startup.