I thought I'd kept you updated on the librttopo development.
To recap: librttopo is a streamlined and thread-safe version
of liblwgeom with its own release cycle and reduced
dependencies/functionality, sponsored by Regione Toscana
to reuse code improved by past investiments in
PostGIS-independent packages (mainly Spatialite).
Given other liblwgeom users currently exist (QGIS, Fineltra)
there's a possibility they will want to switch from liblwgeom
to librttopo to avoid unnecessary dependencies, gain thread-safety
and possibly expecting to more frequent bugfix releases (although
there's no clear plan at the moment about releases).
In its current incarnation, the librttopo library cannot fully
replace liblwgeom in PostGIS itself, due to postgis-specific
functionality we need and currently only find in liblwgeom, but
shall we need thread-safety or any future improvement that will
land in librttopo we could consider using it for parts of the
functionality (for example the topology support).
The API is kept intentionally very similar to the liblwgeom one,
for ease of switching and initially sync'ing between the two.