Hello, as an old user of comix, I think I can agree that mcomix was a fork well motivated and could improve greatly comix which was really nice but with no further improvements. But comix had the great quality of being quite stable. I cannot say that much for mcomix. It happens often to me that mcomix stays stuck, with UI not responding, prevent message-less crashing or such things that could really reduce the user experience.
My message is to ask you to publish stable version. Improve stability can take several way : improve the internal architecture of mcomix, track bugs or wrong design in the UI, factorization of code, etc.
Being a python programmer on my spare time, I will be glad to help you improving mcomix, but I am not sure what could be done at a first task, and I think you mcomix developper are more able to see what are the weakest points in the mcomix soft. So thank you to read my message, I hope you will help me to enjoy mcomix again much more !