Little to no detail at all.
And my prediction came true! They are really alien looking and part of a new biome (and either a fungus or they live with a bunch of other fungus)!
Neldonax also predicted they would become a fungus and be made of Netherwarts, which they are!
I don't agree with removing Poisonous Potatoes, as they already add a (very minor) challenge and you just said you want a challenge. Silverfish already spawn in Extreme Hills biomes so if you build there with stone I guess you already have a chance for Silverfish to burrow into your house.
You are indeed able to place Item Frames on the top and bottom of blocks.
As @erictom333 stated, "Why not?" isn't a reason for something to be added. Also, how would flowers work like crops? Do they have seeds? Do they have growth stages?
No support until less confusing details are given
As a last note, the Small Suggestions Thread is a thing, I recommend moving your post to their as this is a one sentence suggestion that should belong on that thread.
I think the nether should be split into different biomes. These new trees should be really alien looking and probably a fungus, and part of that new biome. The biome shouldn't be that common, though.