Speed art is pretty amazing. I haven't taken a look at the channel yet (so I cannot comment in a good critique towards content) but one way to expand subscribers is to network heavily with other channels with similar number of subscribers. Especially if there's a mixture of audience interest between them. Think about a context between you and another someone who draws speed art or has subs who might be interested in your work as well.
Community networking functions well for everyone involved and often leads to an overall increase in not just subs, but interaction with them.
Basically what ohBeestly said, try making BG's for bigger channels that you know get a lot of traffic or potentially can get that traffic in the future. Usually Partnered BG's that help you the most if you have yourself in there banner. That's the only way I see GFX channels get big, and maybe a video at least every 2-4 days to stay active.