From what you said - so this tool right from the start should be better than paid texture packer and with some additional options that better and free also and open-source - then maybe.. maybe - you will pin it? Right?
My reply is that there are other tools paid and closed source, free and closed source, free and open source, etc.
Can you post link for such open source sheet packer with guy that looks like texture packer?
Also, again here I don;t understand why you taking into account not open source and paid products?
All them out of category because this - free and open sourced.
You know, when you have enthusiasm to develop some free tool you would need users feedback that will inspire you and give strength to move on and develop best tool ever.