The pre-order section is still there ("Top Pre-Orders" -> See All). The problem is that it can no longer be sorted by release date like in iTunes. It always seems to sort by popularity.
But I agree that the TV app leaves a lot to be desired compared to iTunes, and not just the Mac version. What I really miss is an option to only see content that I actually have access to (through subscription or ownership). Instead what you get is essentially a giant advertisement for stuff you can buy, and finding stuff among the clutter that you can actually watch is difficult.