In 2008 I attended a two day symposium that was organised by IBBY or SCWIBI South Africa where international literary agents and publishers were flown out to discuss market trends and meet local children book authors. A question was posed to a UK based publisher asking who dictates the market, the market or the publisher? He responded that it was the market that dictated to the publishers.
My take on that is that the publishers will take on manuscripts that the market wants and not be to keen to take on anything that is nothing but certain. If that is the case then how can anything new or revolutionary find its way into or create a new market.
To self publish, one has to write about that which the market is used to , or to be so bold and to believe in yourself enough to ensure that what you write about might have enough substance to alter or create a new market. To accept that it might not be well received at all and still happily accept the costs is also a must.