Scrum is a framework. You can use it to manage lots of things, including complex product development. Scrum is defined in the Scrum Guide and consists of roles, events, and artifacts, and a set of rules that bind them together. It is based in empirical process control and bottom-up thinking.
The latest Scrum Guide was just released by me and Jeff, and is posted on Scrum.org. Some things like release planning, sprint tasks, and burndowns were removed from the formal definition of Scrum. They were removed because they weren’t Scrum. Are they useful? Absolutely! But it became apparent that these weren’t Scrum when people proposed other techniques that were equally effective. We certainly don’t want people to feel restricted or constrained from other effective practices if they use Scrum.
You should feel free to continue to use burndowns (Sprint and Release), to do release planning, and to commit. Do anything that works within the Scrum framework and aids you in doing your work, building complex products.
You even feel free to do things that aren’t coherent and consistent with Scrum. You are free to do continuous flow, but if you choose to do it without increments and iterative time-boxes, you aren’t doing Scrum. You are free to assign tasks to resources based on their capacity, but then you aren’t doing the self-organization required of Scrum.
We give you permission to do anything that you want. The Scrum Guide will help you understand whether that is Scrum or not. The results will help you decide whether that is a wise practice or technique, or not.