The CDATA is only to maintain the XSL well-formed, since I close fo:flow on another template,
Opening and closing XML tags within different XSL templates is bad practice. You'll need to redesign your XSL stylesheet or run the XSL Transform as a separate process, serialize the resulting FO and then present the FO to FOP.
the tech is good, maybe dev team implement a SAX over the stream from XML+XSL transformation option, this is the feature that I mean.
This isnt very clear, but if you mean serializing the result of the XSL transform before processing the FO then I wouldnt see this as a desirable feature for FOP. Mainly because it will slow down processing. If users require this functionality then they can implement it themselves very easily as I suggested above.
Note that this is to reduce memory consuption.