We're lucky enough we even have 28 episodes on DVD. Full House and Seinfeld are both one of the very few old TV shows to be completely released on DVD, and no episodes of Family Matters have been released on DVD. It is just as likely that Season 3 will come out as any season of Family Matters will come out.
True blood season 2 came out on DVD in the U.S. about 1 month before season 3 aired. I assume that season 3 will come out on DVD about 1 month before season 4 airs. I would find out when season 2 came out on DVD in Australia and assume it will be about 1 year from that time. Apparently it is coming out just after Christmas, apparently