I think the problem of this game is the lack of a good project leader.
If I read the reports from the devs -and assume they are sincere- then the problem sounds an awful lot of delay because of feature creep...
Every time they want to add another good idea to the pile, which makes it more complicated and pushes the release day farther away.
If you look at Sierras work, you will notice that she loves to do a lot at once and also loves to try out new stuff in her games.
In NN she was more careful, but when they started with KoD, she made an ambitious plan for the game AND switched the engine up.
If we assume that she and Nomo parted on decent terms, than we can assume that he has a similiar mindset.
Since images are often the bottleneck in this kinds of games, him also being the creative lead slows down the ammount of sex scenes. Introducing new characters -which he needs to design- and adding more background images increases his workloud further.
So all in all, I think they mean what they write but their constant attempts to make the game even better is breaking their backs.
If I compare this group with Venus Noir (the guys behind Seeds of Chaos) you can really see the difference.
Alioch seems to be a competent project leader, he coordinates and delegates writing and imaging and releases the updates on time. He also seems to have a good sense for cut-off points. Also VNs decision to release the versions with pictureless sex scenes really helps to allow the players to see the progress of the game - and the fact that images really are a bottleneck.
An example for ambitious solo-projects would be Luxee and Darktoz. Both are not the fastest but their supporters are well informed because both give their status often and are honest with their progress (and problems).
And lastly, to examples of games that are.. not well managed and still manage to make timely progress:
Sierra Lee herself is an example, she constantly starts sideprojects, but somehow keeps her updates more or less stable.
But he is a writer first and foremost and inserting her in a project that needs more than her (impressive) writing speed is a dangerous gamble.