See https://github.com/sciurius/perl-Data-iRealPro . It is not a WYSIWYG editor but it supports a simple textual form to write iRealPro and converts it into 'real' iRealPro.

For example:
Code:
Song 1: Ik Zie Jou (Trudie van den Bos)
Style: Medium Swing (Pop-Slow Rock); key: C; tempo: 180; repeat: 3
Playlist: September

{T34 A- ___ | _ x __ | B- ___ | _ x _ <4x> _ }
{    A- ___ | _ x __ | F  ___ | _ x _ <3x> _ }
|    G  ___ | _ x __ | _ x __ | _ x __       ]
_
It is not consumer grade software, but works for me.