It is very likely that m3u to wpl conversion is only related to a transformation of two different playlist formats, namely standard MP3 playlist (.m3u) and Windows Media Player playlist file (.wpl).
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.
But you can of course also use any of the available playlist managers that are specially designed for playlist editing and conversions.
Updated: April 6, 2017