(Even Roualt here)

I see fossil head contains WKT definitions in srs/srsinit/epsg_* with TOWGS84[] terms in them. Those were useful in a GDAL < 3 & PROJ < 6 world, but they are now a nuisance with GDAL 3 and PROJ >= 6 as can been seen in https://github.com/qgis/QGIS/issues/34992#issuecomment-598392777

I'd suggest that the future of Spatialite no longer contains them since it will likely be more likely deployed with GDAL 3 and PROJ >= 6

Hi Even,

supporting a +towgs84 term in "old style" geodesic strings contained into spatial_ref_sys is absolutely intentional.

here is a short rationale:
1. when spatialite is linked against PROJ.6 or PROJ.7 all geodesic definitions are
   always retrieved directly from the PROJ own sqlite DB
2. so the old geodesic strings in spatial_ref_sys are still there just to support
   the case when spatialite is linked against some obsolete version of PROJ,
   and in this case defining +towgs84 is absolutely required in order to
   preserve a fair historical coherence.

future perspectives: when old PROJ versions will be reasonably disappeared, 
spatial_ref_sys will become just a plain dictionary (SRID, auth_name, auth_srid 
and ref_sys_name) mainly intended to support Foreign Key constrains in 
geometry_columns, but will no longer contain any geodesic data at all.