I setup the promotion for a set of around 100 users, set the last active timestamp for all 100K users to the current time & manually ran the script.
It bailed out with an out of memory error.
Allowed memory size of 134217728 bytes exhausted (tried to allocate 91 bytes) in /home/xxxxx/xxxx_html/library/Zend/Db/Statement/Mysqli.php on line 304, referer: http://xxxxxx/admin.php?cron/
I guess this is related to the deleting users out of memory bug when it tries to load too many users at once.
I know it'll get marked as a future fix no doubt, but I thought I'd mention it anyway.
That said, unless it loads the details of all 100K users in, I fail to see why it should bail out with only 100 users requiring to be promoted. Its not beyond the realms of possibility that this could happen on a large & busy forum anyway.