As a CS major i can tell you that release dates are a huge problem is the Software industry. The video game industry is even worse. In the industry proper, you have crunch time. 60+ hour weeks to "polish" the game for release. This leads to something called burn out, the point when working at a game company is closer to hell then heaven. If you make modders have release dates, you will not get crunch time. You will get abandon mods. While they will make the release date, that will be the last update you get for the mod. Sometimes you will have someone maintain the code, but really do they also update. Look at buildcraft, it has been a long time since that was abandon, it now just gets compatibly updates by the crowd sourcing, with Sengir and Lex overseeing.
Please do not put release dates on the devs. I loves these mods and don't want to see these people burn out.