That simply doesn't matter. Tumblr just needs to succeed in ANY slice of the market it can find. A small slice would do nicely. The best bet would be the slice

That simply doesn't matter. Tumblr just needs to succeed in ANY slice of the market it can find. A small slice would do nicely. The best bet would be the slice it originally appealed to, with its original kinds of content, in the original medium it was in.