Czekojin, reinstating passing through enemies via tumble (Shadowform) would be a vast improvement when you are ethereal - it also makes sense thematically - your rogue is in a gaseous form.
Reworking "From the Shadows" also would make sense as it's basically neither use nor ornament (at least for an assassin) it seems only half-completed. It should have allowed controlled movement or you to pass through enemies.
Exploring the; not being automatically detected by monsters with Tremor Sense, was semi-interesting. Albeit not without issues; simply because if the current stealth system wasn't as faulty, it'd be less important...
At least it was planned as a Level 30 requirement; so there less chance of people with fantastic responses saying: Invisibility doesn't work, Sneak is broken, why can that Champion see me via 'True Seeing', etc. Albeit until the Character levels-up and attains that ability; you've still got the same exact scenario and conditions regarding the current "faulty" stealth system.
There were plenty of interesting ideas pitched in like mechanical "bug bombs" some were more feasible than others.
If you want to see all the main U51 Shadowdancer Preview "lively" debates:
In this thread you've probably given better overall communication then we got from the developers dealing with the Shadowdancer planning during those three previews. :-)