The Next Stage in Composition -- McIlroy

But most significantly, XSL-FO will catch on because the adoption of XML (and, more importantly, XSLT) has become so widely entrenched across all industries, and has the unequivocal support of all of the largest and most important vendors across the business process landscape.

Working with XSLT moves a developer a big step closer to being able to implement FO, and that's a significant undercurrent of experience and energy propelling the standard forward.