Here's the deal breaker, the fly in the ointment, that exposes the flaw in this particular ICO business model, (at least prima facie):
As a writer you hope for more sales. So, more tokens is your joy.
But, as a token holder, you revel in scarcity. The lesser the number of tokens, the costlier they become; so, in direct contradiction with your first joy, the lesser the number of tokens, the more valuable they become.
Apart from these cross-purposes, the essential fact remains that a published book, especially when it's online, depreciates in value. So, invariably, not only will the number of tokens remain more or less stagnant after the initial release, they will also rapidly dip in value. And, we haven't even factored in online book piracy into the equation yet.
Happy investing, DYOR!