Looks interesting. Along with the other software mentioned here I hope it is ok to plug Easy Data Transform[1], which is also written in C++/Qt. It can read and display CSV, fixed width, JSON, XML and Excel data files. But it also has extensive capabilities for visually transforming data (join, filter, sort, interpolate etc) without programming[2]. It is commercial software for Windows and Mac[3] with a free trial.

[1] https://www.easydatatransform.com

[2] With the option to use Javascript or regex, if you need it.

[3] Not enough demand for a Linux version, so far.