It's very possible it's meant to prevent guaranteed setups. Keits might be hanging around and can chime in on it. Since KI has been part of games with gold I have noticed more players in ranked matches, wonder what the total amount of new players will look like by end of January.
You cannot hit someone with an unblockable attack if they are already in blockstun. They'll simply be allowed to block it.
So even in the worst case, where you time an unblockable to hit someone 1 to 4 frames after the blockstun from a grenade ends (which totally works), it is possible for them to backdash or reversal out depending on positioning.
Check out Bastfree's extremely high tech Orchid stuff to learn more.
Also, start watching weekly tournaments with us! You'll learn a lot and have a great time. Today at 5pm PST is the Top 32 Killers Showdown. I'll tweet out the stream link later but its usually on twitch.tv/killerinstinct
Edit: Re Combo Assist.
Combo Assist doesn't remove the 'perform under pressure' aspect of fighting games at all. All it allows you to do is get through the most trivial type of combo in the game (a type of combo that is never dropped in mid to high level play) with a hair less practice.
Pressure to perform a massive list of much more interesting skills remains totally unchanged;
-reversals
-anti airs
-spacing properly
-keeping yourself out of the corner
-cornering your opponent
-reacting or anticipating in footsies or neutral
-learning and exploiting matchup strengths
-learning and minimizing matchup weaknesses
-blocking properly
-shadow countering
-opening your opponent up to even start a combo
-managing your meter
-managing and using your instinct
-performing manuals, links, juggles, setups, oki, etc
-combo breaking
-counter breaking
-manipulation of your opponent's actions
etc etc etc. The list goes on and on.
If you were struggling to get through the "golden path" combos (Opener, Auto Double, Linker, Auto Double, Linker, etc, Ender) in the first place, this mode was designed to get you to the thinking part of the game quicker, so you can engage in all of the things (and more) that I listed above.
And yes, the dev team will be working to solve bugs and weird Combo Assist Only Option Selects that appear.