GEOS 3.5.1 & 3.6.0 have been released, since the changes in 3.6.0 don't
look very worrying upgrading to 3.6.0 for stretch seems like the best
option (since a transition will be required for either).
One of the major changes is the removal of the PHP bindings which have
split off into a separate upstream project. As discussed before, initial
packaging is available for php-geos, but I wonder if there is an actual
need for the package. 
Since only the reverse dependencies C++ library need to be rebuilt, the
transition will be limited. But based on the rebuilds so far, we may be
better off transitioning to 3.5.1 instead, since the projects that rely
on the C++ API pretty much all FTBFS with GEOS 3.6.0.
ossim (126.96.36.199+ds-5) FTBFS due to changes to the GeometryFactory:
geos::geom::PrecisionModel*, int)' is protected within this context
m_geomFactory = new geos::geom::GeometryFactory(pm, -1);
Reported upstream: https://trac.osgeo.org/ossim/ticket/2382
osmium (0.0~20160425-e2e4368-2) FTBFS due to the same issue.
Reported upstream in: https://github.com/joto/osmium/issues/100
Since osmium has been deprecated in favour of libosmium, a fix for this
issue is unlikely. But perhaps the fix is easy and we can just patch it.
libosmium (2.9.0-2) FTBFS due to the same issue too.
Reported upstream in: https://github.com/osmcode/libosmium/issues/168
osm2pgsql (0.90.1+ds-1) FTBFS likewise.
Reported upstream in: https://github.com/openstreetmap/osm2pgsql/issues/634
To double check the reverse dependencies only depending on the C API
I've done a full round of rebuilds after all, and those all rebuilt
libgeos-c1v5 (3.5.0-4) -> libgeos-c1v5 (3.6.0-1~exp1)
libgeos-3.5.0 (3.5.0-4) -> libgeos-3.6.0 (3.6.0-1~exp1)
The status of the most recent rebuilds is as follows.
basemap (1.0.7+dfsg-4) SKIP (no C++) / OK
librttopo (1.0.0-1) SKIP (no C++) / OK
ossim (188.8.131.52+ds-5) FTBFS
python-shapely (1.5.17-1) SKIP (no C++) / OK
spatialite (4.3.0a-5) SKIP (no C++) / OK
gdal (2.1.1+dfsg-5) SKIP (no C++) / OK
pyspatialite (3.0.1-11) SKIP (no C++) / OK
spatialite-gui (2.0.0~devel2-4) SKIP (no C++) / OK
spatialite-tools (4.3.0-2) SKIP (no C++) / OK
grass (7.0.5-2) OK
imposm (2.6.0+ds-3) SKIP (no C++) / OK
libosmium (2.9.0-2) FTBFS
mapcache (1.4.1-3) SKIP (no C++) / OK
mapserver (7.0.2-1) SKIP (no C++) / OK
osgearth (2.7.0+dfsg-2) SKIP (no C++) / OK
osmium (0.0~20160425-e2e4368-2) FTBFS
pdal (1.3.0-1) SKIP (no C++) / OK
postgis (2.3.0+dfsg-3) SKIP (no C++) / OK
osm2pgsql (0.90.1+ds-1) FTBFS
osmcoastline (2.1.4-1) SKIP (no C++) / OK
pyosmium (2.9.0-1) SKIP (no C++) / OK
qgis (2.14.7+dfsg-2) SKIP (no C++) / OK
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