When you open .m3u playlist in Windows Media Player, you have the option to save it to the program's default playlist file format - WPL. Probably should also be possible with other media players that have a broader support of playlist formats.
Convert MP3 songs playlist file to Microsoft Windows Media Player playlist file.
We have found 2 software records in our database eligible for .m3u to .wpl file format conversion.
Microsoft Windows software - convert m3u to wpl on Windows
The default multimedia player from Microsoft Windows
Convert from m3u file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned m3u to wpl. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Advanced playlist creator and manager