Two models we've seen

Centralized team working on multiple sites
 

Geographical teams working on shared infrastructure

Create per domain base pages

Flexibility takes a frontseat

less surface area to train, so you can spend more on your complexity budget

Expect more from the teams 

Force people to use standard items

Standardization is more important than flexiblity

Assume low skill levels and focus on simplicity

Double down on user groups and aggressively limit edit status

Snippets are extra useful  - lock down permissions for them

As much as possible, set good foundational data ( e.g tags)

Keep the markup the same as much as possible

Expect that you'll have a different base styling per domain

Expect that things will look different, but you want to keep the functionality as similar as possible

Try to do site specific work in CSS

This is the easiest datatype to deal with so use it as much as possible

Rich text improvements are often the most portable cross domain

You will forever lose the ability to make cross domain changes if you allow this

Create headers dynamically from pages below site root

Footers inevitably end up different

Meta stuff is all different

Probably need a god object to store logos/filter custom django objects from

Swappable Sites model

Publish notification email per domain