That's nothing to do with different episode lengths though is it? As someone else pointed out what we're getting now is a 45min or a 55min episode, where they're not 10-15min of filler so it's hits the 60min mark. What you're talking about is a much longer format and world building, which is a different thing altogether, it would be great to have much longer format shows, with proper world building, but they have enough talented people and enough good material to make that happen.
Let's face it modern TV shows have enough trouble filling 6-10 hours, and a lot of is dragged out into walking and fetch quest simulator - and a lot of shows are just whole lot of nothing from start to finish.