It very much depends on how you calculate dps, rdps and personal dps and then it also very much depends on what you consider varible.
If viable is able to do as much dps as mut or combat then no sub is not viable. Even if you tot a top dps target spam hemo and calculate the +rdps from tot and hemo you are still going to be 700-1k dps behind mut and combat in any tank and spank fight.
If you want the most damage from sub then you need a pretty melee heavy raid, a top dps with no agrro problems and go slow axe/mace sword and spam hemo. On top of this you also need a crit heavy group and be ready to weapon swap for shadow dance.
The reason why you dont go back stap is because you need the short rupture to be able to shadowstep->rupture for more damage.
Now if we ever get an insane movement fight sub might be viable because of shadow step but even with all the movement on putricide mut or combat would still be better. So if you realy want to spec sub and dont care about max dps then its more viable after the patch BUT you should still know you are nerfing your damage and if you dont got atleast 2 parts t10, tot every cd, shadow step every rupture then you are nerfing your damage ALOT.
And to your last question about more changes? How the fuck should we know
Its a fan site not a forum for clervoyants (how ever you spell that) trying to guess the future. My guess is that they are done but you never know the only thing you can be sure of is that if we see a change on the ptr its going to be on the front page.