Here is an update. At some point along the line, the bug referenced by jgm above has been remedied, which rendered the filter non-functional. Here is the current working script.
Joel
System:
Windows 7 Pro
ghc 7.10.2
Pandoc 1.17.1
R 3.2.3
RStudio 0.99.863
import Text.Pandoc.JSON
pgBrkXml :: String
pgBrkXml = "<w:p><w:r><w:br w:type=\"page\"/></w:r></w:p>"
pgBrkBlock :: Block
pgBrkBlock = RawBlock (Format "openxml") pgBrkXml
insertPgBrks :: Block -> Block
--insertPgBrks (Para [RawInline (Format "tex") "\\newpage"]) = pgBrkBlock
insertPgBrks (RawBlock (Format "latex") "\\newpage") = pgBrkBlock
insertPgBrks blk = blk
main = toJSONFilter insertPgBrks