Still here just now in the top bar.
and if it ever disappears from there a fallback is to look for it at http://meta.gis.stackexchange.com
The only announcement of this change seems to have been made on Meta of StackOverflow.
The announcement was made on the Stack Exchange blog: http://blog.stackoverflow.com/
A New Top Bar for Stack Exchange
The top bar of a Stack Exchange site has always been a bit of an odd place. It somehow combines user info, navigation, search, and a one-size-fits-all popup that includes hot network questions, a list of 100+ Stack Exchange sites, ...
Having just been through a number of Close Votes where the subject was definitely on-topic I also agree with the no longer relevant suggestion. The questions were not off-topic according to the purpose of this site, they were merely old or an answer had been discovered by the Original Poster (OP). So, pedantically, I didn't feel I could vote to close the ...
I agree with the intent of this new custom Close reason being made available for Meta questions but I do not think that it needs to be implemented because we can already propose closure using the Other category saying:
This question is about something
which is no longer relevant because [give reason].
I suggest that if a question in GIS Meta is on-topic, unanswered and it is believed to be "not relevant anymore", then there should be an answer explaining why.
That would be likable to avoid discussions about why a post was marked "not relevant anymore" in cases the reason is not so clear (and people could vote in the answer agreeing with it, or not). And ...