Built a way to make an export track changes to a branch.

git annex export --tracking master --to myexport

That ties in nicely with git annex sync:

joey@darkstar:~/tmp/bench/a> echo hello > foo
joey@darkstar:~/tmp/bench/a> git annex add
add foo ok
joey@darkstar:~/tmp/bench/a> git annex sync --content
commit  
[master 8edbc6f] git-annex in joey@darkstar:~/tmp/bench/a
 1 file changed, 1 insertion(+)
 create mode 120000 foo
ok
export myexport foo 
ok                          
joey@darkstar:~/tmp/bench/a> git mv foo bar
joey@darkstar:~/tmp/bench/a> git annex sync --content
commit  
[master 3ab6e73] git-annex in joey@darkstar:~/tmp/bench/a
 1 file changed, 0 insertions(+), 0 deletions(-)
 rename foo => bar (100%)
ok
rename myexport foo -> .git-annex-tmp-content-SHA256E-s6--5891b5b522d5df086d0ff0b110fbd9d21bb4fc7163af34d08286a2e846f6be03 ok
rename myexport .git-annex-tmp-content-SHA256E-s6--5891b5b522d5df086d0ff0b110fbd9d21bb4fc7163af34d08286a2e846f6be03 -> bar ok