It needs to be out before all these blockbuster titles around the holidays.  COD, AC, BF, and many more will come out in October/November and PS360 will most likely have them too.  It could help out significantly with software sales of the new console and hardware sales if it can be out before these games release because people aren't gonna wait for them.  Look at how WiiU got almost no sales of AC and COD this past year.  Sure the crowd is different, but the fans of those games also had already bought them for other systems.  Watch Dogs could end up being like that if it comes out in October and PS4 isn't here till November.  Worse if Nextbox launches first it will become the platform that everyone's friends have these games on so they will lean more towards getting that.  This is a big deal I think and it would serve them well to get out ahead of the holiday titles flurry.

How important is this aspect do you guys think?

Pretty important but not major.

What will sell the systems in the long run will be the exclusives.

Yeah, it should go head to head with GTA V.

it should have GTA5 on it.  I know I would buy the PS4 version with likely better framerate, resolution, and load times.  Not to mention all the extra social features like sharing gameplay moments would be awesome with the random mayhem of a GTA game.

It's not the most important aspect of launch, but I can see where you're coming from. Doing this might give the PS4 more of a chance Multi-Plat wise.

It should, but I'm doubtful about it. It wouldn't surprise me at all if the rumors are true and Microsoft gets at least timed exclusivity on the next gen version of GTA.

Meanwhile, the next COD being on PS4 is much more likely.

In the long term there will be a lot more things that determine how PS4 sells. However, getting it out ahead of the late October - early January sales rush is very important. I think that a major reason why PS2 got off to such a hot start was the October 26th launch in the US. It gave it time to build up awareness, and perform better thoughout its first holiday.

To me part of the reason 360, PS3, and WiiU got off to so slow of starts is due to launching to late into the rush. Launching on Black friday week just seems like a major disadvantage. Why would you launch on the week that every competing device is going to have its best offer of the year?

My hope is that Sony and Microsoft will have these consoles ready by late September - early October. I think that would give gen 8 the best possible start, and lead to a much healthier ecosystem. Like the OP said, the more people with next gen consoles, means more friends wanting to make sure they have the console to play together. That sounds like better sales late 2013 = better sales all of 2014.

If the next Xbox launches with Call of Duty before PS4, it will end up bad for Sony

What!?  I haven't heard a single rumor to that effect and wouldn't that cut their sales in half?  Hell San Andreas sold more on PS2 alone than GTA4 did multiplat so I highly doubt that.

Nah its gonna be November. If anything MS is more likely to do September.