While reading the Wikipedia article on rice pudding, my curiosity has gotten the better of me. Clearly, any flavourings, spices, toppings or sweeteners will be optional and the article also explicitly states that eggs are optional.
Referring specifically to their section on the UK variants, it seems to be the case that the minimal set of ingredients is either milk, rice, and cream or milk, rice, and butter. This has me quite surprised, as both experience and the earlier parts of the article have suggested that milk is normally a good enough substitute for cream, so I see no reason why it wouldn't be possible to make rice pudding with either just milk and rice or just rice and cream.
However, I've yet to see a recipe for either of these two minimalist options. Is there any practical reason why this wouldn't work?