DOS style is different from DnD stealth because DnD relies soley on checks while OS2 is about positioning.

T2H: you need to think of stealht in OS like you do in DnD, its a standard hting everyone can do.
the scoundrel isnt the backstab class, and the reason its not very good in OS1 EE is because it used to be OP so they nerfed it hard.
Basically mid combat stealth is not the point, the point is to set up extremeley potetent alpha strikes.

in DnD it mostly works the same, at least in later edition, going invisible during combat is something you only realy see in 4E outside of wizards.

either way, i hope they include sight lines in this one. It not mattering just doesnt translate well to a PC game.
5E is a very simple game, including things like facing is not the intention for WOTC, the idea is that basic 5E is a skeleton of a game that you can add on to, you can clearly see that iwth the inclusion of feats as an optional rule.