General FO Implementation Feature Query: Balanced Page

We have a client for whom we're trying to use XSL-FO to format some
books--these are mass-market fiction and non-fiction books, as opposed
to say technical documents. XSL-FO is probably not appropriate for this
application but we're trying anyway.[1]

One requirement that has come up relates to the typography of the
finished pages: when lines from one page have to be moved to the
following page to satisfy widow/orphan constraints, the client wants to
have the content of the first page adjusted via kerning and line height
tweaking so that the vertical extent of the lines on the first page is
equal to the vertical extent of the lines on the next page.

I know that this is a level of sophistication that is both technically
challenging and beyond current FO implementations but...

1) Is it technically possible for a non-interactive FO implementation to
implement this type of requirement?

My assumption, based on little more than hunch (I've never tried to
implement formatting beyond basic line breaking), is that it is
technically possible but quite difficult to implement and quite costly
from a performance standpoint.

Eliot
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[1]XSL-FO is probably inappropriate because these books will tend to
have layout-driven requirements that XSL-FO and current proprietary
extensions cannot address, such as per-page footnote numbers, just to
name one.

--
W. Eliot Kimber
Professional Services
Innodata Isogen
9390 Research Blvd, #410
Austin, TX 78759
(512) 372-8122

eliot@xxxxxxxxxxxxxxxxxxx
www.innodata-isogen.com