None of us appreciate having our ongoing effort characterized as 'stalled'. Everything in the commit log, Jira and Confluence activity streams belies that. More people are actively involved in improving Clojure than ever.
As for CLJ-688 - it's an enhancement request. Do you think every idea for an enhancement that anyone has should make it into Clojure? I don't - it would quickly become a huge mess. If not, then someone has to look at everything and decide.
Yes, there is a backlog from when it was just me, and it will take a while to whittle down. We have finite resources and have to prioritize. I can assure you we have more important things to concentrate on than your negative index substring enhancement, and are doing so. You'll just have to be patient. Or, if you insist, I'll just reject it now because a) IMO it's goofy, b) you can make your own function that works that way c) we don't get a free ride from j.l.String, d) it begs the question of negative indices elsewhere...
Want Clojure to be a free for all? - Sorry.
Can't cope with the necessity for prioritization given finite resources? - Sorry.
Want top priority? - Sorry.
tl;dr: This blog post is the idle chatter of people who are not involved in the Clojure development process in any significant way. Lau has never submitted a single patch. Apparently his free lunch isn't arriving fast enough.