It's not that I'm some guy undercover, keeping people from this site but Guitartricks main competitor Jamplay is going to bring out high quality bass lessons somewhere this year. Even David Ellefson from Megadeth is going to do beginner lessons on their website. They are planning on releasing full beginner courses transcending into more advanced stuff and songs.
But those lessons aren't up yet. You should check their website from time to time or subscribe to their newsletter to keep being updated.
It's a fun option, we have considered it but it means taking time away from guitar-centered material and we still have a lot of ground we'd like to cover there. Maybe in the future?
Just to throw my 2 cents in i have been a member since 2009 and have learned alot but there is soo much to learn. But also i started to learn Bass as well and i think a sight that can help me learn both bass and guitar would defenlty get my attention. My be something to thing about. I bet there are alot of guitar/bass players looking for a sight to fill in the void. My get ahead of a trend rather than follow one.