I'm not sure it is for GameMaker.
In response to the iPad app, I do't belive iOS can handle vector graphics for games. The Universal apps can contain multiple images though and select the proper image for the right device. They can also scale. hence why the Universal apps are so large in size. The squashing from graphics would be because the iPad is a 4:3 ratio while the iPhone is 16:9 ratio (more or less). Chances are, the graphics are scaled higher for iPad resolution and shrunk by the OS to fit the smaller screen instead of using different images.
Then we get into the issues with mobile. Sure, Windows 8 might be okay, but iOS and Android would not. Playing games through portable browsers wouldn't work. Also, I'm sure it would wreck havoc on CacoonJS.
It, again, was said before, but with the current state of PCs, why care about size so much? I know it seems like a lazy thing to say, but broad band connections are much faster and hard drive sizes are much bigger. The game, if targeting node or HTML5 browser, can always be made in higher res (1080P) and downsized by the system. That would produce FAR less overhead then running SVG animations and transforming collisions on the fly, even for older systems. Also, speaking of older systems, they could handle downsizing rastor images much easier than SVG.
If the target platform is going to be mobile, the game dev will design with that in mind, or port accordingly. It's lazy not to and makes for a bad experience on the player's part. Also, mobile can't do SVG.
At the end of the day it's the right tool for the right job. In this case though, since C2 targets an HTML 5 environment and uses wrappers to port to other platforms, I can't see where a tool like SVG would be beneficial at all. I hate to say it, but if it comes to a point where SVG is a required tool for the job, maybe a different IDE or platform should be used (in this case Flash)?
Come visit and play Blast Box!