To us western fans it may seem strange to see YN returning after all this time.
But… was it really forgotten about in Japan?
As you may know, Yume Nikki is one of - if not the - most iconic RPG Maker Games ever created. And it lives on in fans' and artists' hearts. Fanworks have been created ever since. Not as many as there are those based on hyped shows and games, but quite a lot compared to other RPG Maker Games at least.
Speaking of other RPG Maker Games, there is quite a huge fanbase of them in Japan.
Events by and for fans and circles have been held; "Try&Re:save" in 2015 and "Try&Re:save2.0" in 2017; "Freedom Game" 1-7 with the first one in 2016. And a Yume Nikki-specific event called "Mars Picnic" in 2014. The only other game with an event dedicated to it solely is Ib with "Rose of Museum".
The dimensions of these events compared to Comiket and others are unknown to me, but there sure had to be quite a lot of people attending them so the organizers see it's safe to plan a next one.
Yume Nikki is definitely one of the best-known RPG Maker Games within Japan, along with Ib and Gokuto Jihen, and the newer games Satsuriku no Tenshi and Higyaku no Noel.
The game with the most Doujinshis (~500) is obviously Gokuto Jihen with it's male-only cast; resulting in a huge percentage of 18+ Yaoi, which is quite popular for some reason. The second place takes Ib with circa 300. On the third place is Yume Nikki with circa 100.
It's quite obvious to see these three of all on the top, given the amount of qualitative original content to heat up the creativity.
Since there are always Yume Nikki-centered doujin circles at Comiket as well, it would be possible that KADOKAWA picked up the idea for the new project from there.
Project Yumenikki is, as far as I know, a kind of doujin circle as well, a group of fans, so to say, just for some reason more official.
I just wanted to share that information with you, since I remember someone was wondering about it and I think it's quite interesting to know.
-and other sources about physically released doujinshis