Immersion is the better word for it and it is critical, beside how hard can it be? (and no not a car related quote at all.....)
I wouldn't go as far as saying its critical since there are other things which are more important for them to add. However I can't see it being very difficult. In my opinion it should either be a matter of switching the cloak skill from system only to sector and system, or just duplicating the skill and changing the new one to system only.
Of course I don't know their systems so I can't say for certain. It may actually be harder then we think.
I don't think there is any significant difference between sector space and normal space maps. I imagine the cloak ability could be allowed in sector space, there are other abilities that work in both, such as the fire work reward.
In regards to the immersion comment, that is the nail on the head! It would purely be an immersion thing. I think it would be quite fun flying a cloaked Defiant retrofit through klingon space.
Dan mentions in the lastest Ask Cryptic about adding a Territory Control aspect to the game. This would involve the Fed vs. the KDF and would involve both PvE and PvP content. At that time, the ability to cloak while in Sector Space will be a key component in the war. You'll get it then if not before, I'm sure.
Can you imagine how cool that'll be? Silently following in the wake of a Federation starship, waiting for the opportune moment to strike.
Heck, even with allies I can name numerous ocassions where I've had a Defiant or a Gal-X in Sol Sector and wanted, so badly, to do the heroic "decloak and fire" on the nasty Klingons who were picking on the little Ensigns.
"Sir... there's another ship coming in... It's the Enterprise!"