This post is going to be part hypothetical suggestions about way to get ICly okay with the way SIC works, and part OOC commentary on the system.
70 million voices. All the time, except when it's not there. Do you REALLY want that? I'm sure Johnny and Slither can code up a stream of NOISE that will go ALL THE TIME (except when it doesn't) and completely overwhelm your ability to parse it.
Imagine your screen scrolling non-stop as quickly as your CPU can display text. Hundreds if not thousands of lines every few seconds.
You'll lose poses, emits, combat messages, the whole nine yards. But you'll at least have "realistic" experience of what the noise of 70+ million, always thinking people is like.
The flipside of being overwhelmed is the functional system that we currently have.
With the system, your character notices that SIC is out when they notice it is out. "I haven't heard from X in a few minutes." "I want to talk to Y." "I haven't seen that shared key that A and B have been using lately."
I think that the need to type / think commands every once in a while (ch, ct, who, whatever) to 'check' on the network is PERFECT. It shows the addiction to it right there. Some characters are so attached to SIC that they are constantly check to ensure that they have a connection.
To get into some abstract thought here; maybe characters are only aware of those who are nearby or who they have come across, day after day. It's a mixture of psychic energy and a radio transmitter that has been welded into the brain stem and central nervous system. Perhaps the mind subconsciously filters out all the "other" voices and remains aware of those from people whose presence and proximity has the potential to affect it.
There's a pretty commonly accepted theory that the mind can only consciously remain of 7, plus or minus 2 stimuli and / or thoughts at a time. Some people struggle with 5, while others seem to rarely miss anything up at 9. Advertisers use this knowledge all the time to 'overwhelm' the senses and disengage the conscious mind, forcing consumers to rely on emotion and conditioning to 'make sense' of what they are being sold.
Random thoughts about perception and the mind aside, perhaps an awareness of brown-outs can be coded. Maybe some people are SO FOCUSED on the SIC network that they are aware of when it goes out. At the same time, they are UNAWARE of plenty of other things (the dip lurking in the shadows, the same person who has been following them every day for the last week, the fact that the cashier short changed them).
I say if those people want an option to toggle on, let them. And toss in a few penalties to Perception and Intelligence at the very minimum. Maybe even Agility to simulate a lack of attention being paid to their body. (Just like people staring down at their phones and walking are more likely to bump into people, trip over curbs, whatever)
If you've read this far, maybe experiment with your consciousness for a second. Set a timer for a minute, then relax and seem how many stimuli you can maintain awareness of AT THE SAME TIME. The sensation of sitting there. The sound of these words as you read them, unless you read purely visually. The colors on the screen. The wall across the room. That sound over there. What was the first thing on the list? What did you have for breakfast yesterday? What's your best friend's email address? Do you even remember what your room smells like as you're reading, looking at the monitor, following your thoughts....
Yeah, fun. Right?
Are you SURE you want a "real" reproduction of 70+ million people's thoughts in your head?