is that option still planned?
Yes and No.
Yes, it is still a “TODO”.
No, I don’t have time to work on GD recently. (Though, I will fix any critical bugs and review any incoming pull requests ASAP.)
is this difficult to implement in qt?
Also Yes and NO.
No, it is not hard. Change icon size only needs a few lines.
Yes, it is hard. Putting these a few lines into GD requires reading/adjusting existing spaghetti code. Also, making this functionality available to normal users, like providing a config option, requires more work.
Also, can we stop talking technical issues here? You certainly know how to use GitHub’s issue tracker. Not sure if you noticed, but users here mostly don’t care in technical details, and they shouldn’t. (The need for them to care is somewhat a failure 
) I think this post’s primary purpose is for feedbacks. I will just ignore any of your technical comments here from now on, please use GitHub for tracking technical progresses.