Trinkets support would be very nice.

As well as visualization of backpack on player's back and a hotkey (B, for example).

Trinkets is actually already supported in recent versions - you can put Backpacks in your backpack slot and press the B key to access it (perfect prediction)!

I love the idea of backpack visualization, so I've added it in the next release... it's a bit of a budget solution given my lack of modeling skills, but I think it still looks much better than nothing. It supports backpacks in the Trinkets & Armor slot. This will be out in the next release, so let me know what you think! Thanks for the suggestions.

That's great news!

Actually, I've modelled and textured a backpack in Blockbench:

It's only a leather variant, but you can use it for Inmis and re-texture as you like.
backpack.zip