How can I use PGN-Extract to split a multi-game pgn into separate files with just one game per file. With the pgn being named for the opponents? Like opponentA-opponentB.pgn
To a limited extent, you can do something like this already using the -Tp argument which selects games by a particular player. So:
pgn-extract -TpLeko --output Leko.pgn games.pgn
but there is not currently (2018.12.19) a way to have the file names generated automatically from the contents of the source file. Without a way to bound the number of players of interest this would require a lot of file opening and closing for a large input file. Some thought would also need to be given to how player names are mapped to file names.