The problem is that the ppx library is now wrapped. While waiting for odoc integration, the experimental -lib option of ocamldoc seems to do a half-decent job:
where=$(ocamlfind query sedlex)
ocamlfind ocamldoc -sort \
\
-I $where \
-I $where/ppx \
\
-package gen \
-package compiler-libs \
-package ocaml-migrate-parsetree \
-package ppx_tools_versioned \
-ppx "ocamlfind ppx_tools_versioned/metaquot_405/ppx.exe --as-ppx" \
-lib Sedlex_ppx \
$where/ppx/sedlex_cset.mli \
$where/ppx/ppx_sedlex.ml \
$where/ppx/sedlex.mli \
$where/ppx/sedlex_ppx.ml \
$where/ppx/unicode.mli \
$where/sedlexing.mli \
\
-html -stars -m A