In my experience, customers are rarely interested in non-custom software that doesn’t come with support and/or enhancements. So unless you are writing defect-free and complete software, you will end up doing “on-demand” work on your custom software to patch bugs or add critical features. That is, developing your own code doesn’t do much to avoid stressful on-demand work. I suspect the scale and culture of your company is the best way to moderate stressful on-demand work.

But the software I’ve been involved in, even our non-customer specific is still oriented towards large sales and heavy customization. I suppose if you can avoid that, you will go further to controlling your release cycle. The more customers you have, the less they need to pay; the less they pay, the less they expect immediate fixes from you.