Remathilis
Legend
I'm with it, except for the whole biding your time for a surprise attack bit. Too many bad memories of the 2e thief's backstab being totally useless. People fighting back to the wall, or back to back was so common, you'd think everyone in the world had cast protection from backstab 10' radius.
Sadly, those are the common tactics to avoid being waylayed by a lurking foe.
2e backstab was useless for a variety of reasons; it didn't scale quickly enough, it was a horrible pain to set up, and usually worked once per combat if it even did at all. I have no problem allowing rogues some form of 3e-era sneak attack mixed with a few 4e-style movement tricks to gain advantage easy.
What I think Mearls was saying is that a rogue shouldn't get a "sly flourish" style attack where they deal good damage by simply standing there. A rogue needs to be mobile, opportunistic, and willing to use all manner to tricks an guile to set up advantage and get his SA dice.
Put a different way: A fighter can stand toe-to-toe with an orc and deal large damage from weapon choice, strength, specialization, etc. A rogue going toe-to-toe deals crappy base weapon damage, but if he moves, finds weak spots, and ambushes foes, his SA dice easily equal out to all the fighter's weapon focus.