Some "customers" have failed badly at the same attempt already since 2014. Jagex only made less and less quests. This thread showed some of these failed "customers":
http://services.runescape.com/m=forum/forums.ws?341,342,132,65411098,goto,1
OP's quotes on comments of Jmods on quests (Page 1, Post 6) summed up the situation which have not changed in 4.5 years:
"The root of the problem
One can think of various reasons why we are getting less quests (note that this is all speculation, albeit well-reasoned).
First of all, quests take up a lot of resources. Especially now, where quests often have us visit new places that have to be unique. Rite of Passage is extremely expensive according to Mod Jack, and I imagine Fate of the Gods will also have been since Freneskae had an all new non-recycled environment. According to Mod Osborne, five (I believe, may be wrong, but definitely five-ish) quests are usually in development at any given time and quests can take quite a while to make. (up to a year - but that's very rare and only for the WGS's out there really)
Additionally, other large projects also require a large budget, which may well inhibit quest release. Think RuneScape 3 or Prifddinas - these had/have a very large team of developers, designers, Quality Assurance testers, artists, etc. working on them, who would then be unable to work on quests."
The "customers" can demand one thing, but whether the company has the time, resources and budget is another.
Last but not least, one of the Jagex content development team is working on a quest already. It probably will come out this year.