Sims 4 on Mac

I would say YES it would.

I have the Macbook Air Mid-2013 with the i5 Haswell, 4gb of ram, 128gb HD. The integrated graphics chip (the Intel HD 5000) is a beast of an integrated graphics chipset with 1.5GB VRAM!

My model is the same as yours except for yours has a slightly newer processor, but the same graphics chipset and everything else.

Let me just say this laptop is a machine. I moved from a Macbook Pro with an i7, 8gb ram, nvidia graphics etc... and this outperforms it speed wise.. probably part of that is the SSD. I am a power user, so I use it for web design, photoshop, illustrator, After Effects etc.. and it doesn't hold be back one bit. Video Processing could be a bit faster but what more can you expect from a laptop this size!

But this laptop can hold its own as far as games go! If you want the best gaming performance, install Windows 8 on it through bootcamp! I am able to play Starcraft 2, World of Warcraft, Simcity, Fifa, F1 2013 and loaaaadsss of games on this beast of a machine,

Don't expect though to run Sims 4, Battlefield 4 and Crysis all on Ultra and get a solid 60fps. But most if not all games are perfectly playable on this machine. On low-medium (on brand new intensive games) and medium-high on slightly older games.

The Sims 4 doesn't look toooo intensive so I can see this running just fine on the Macbook Air!

I do recommend though if you're installing bootcamp and want to play games on it and like me are limited to the 128gb ssd... get an external/portable USB3.0 hard drive purely for extra file storage and installing games on.
Games take up alot of space, your going to find yourself strugglign to fit OSX, Windows 8, all your apps and files on 128gb. So it always pays to have extra storage. Games run perfectly even though they are installed on the external drive.

Well i've noticed on games with alot on the screen at once, 4gb of ram on the system can be a bottleneck. So i'd say for people who have ALOT of mods installed, maybe that's why it's been a bit laggy on theirs.

As for installing it on MAC, that depends on whether The Sims 4 is even MAC compatible when it comes out. Nobody knows how long you'll have to wait till that happens.

Even if they do make it for MAC, it would still probably run better on Bootcamp windows. And as for whether or not you should get a hard drive or not... you could probably get away without one initially. But if you download alot of films, store photos and files, install programs like Photoshop. You'll find yourself out of space before long, and you'll have to start deleting stuff.

I have a 1TB External connected to my mac where i store all my files, my games etc... that way i can use my macs hard drive for all my essential stuff.