Ever since the first release of vmod_pesi, we knew that this feature
was probably not useful: As explained in the THREADS section of the
vcc / man page, we can not push to VDPs, so the only case where this
could work was when there are no VDPs. The only case pESI itself does
not need any is non-esi, non-gzip uncacheable streaming. Also, the
only case where it made a significant difference from pushing from the
level 0 / front thread was when there are no threads available and the
front thread runs the current include.

Since then, we never encountered a situation where we would have
needed this feature.