I have used ELS for IV and I am well aware that it took a lot of time to make that a great mod. Although I think he is exaggerating - my point is that if he keeps making people wait that much, people will get bored pretty soon. I'm not saying this for myself, because I have already ELS V and I don't really care, I just try to guess because I used to do this kind of things too. I announced something would come out, people would get very hyped for it, I showed screenshoots etc, then when I realized it was going to take too much time to master, I decided to release everything the way it was, but it was too late, people moved on.
And I'm afraid the same might happen with LUM for V, considering modding for GTA V is already pretty dead.
People would rather use something buggy but earlier, than something perfect but years later.