Readiness is something which has been, and will be hotly debated in the agile community. Personally, I love the concept... But Then I was a Business Analyst for years. Consider this scenario; Your development team is plagued with unexpected work, high bug counts and seemly never ending technical debt.. and very little traction on actually moving through the product backlog.
A Nightmare situation.
The morale impacts of constant problems on a team and no progress through the "interesting" work are brutal. The fastest way to drive productivity into the ground. So how did we get here, and where is a good place to start looking to solve these problems? In my opinion: start at the start. Look at the quality contained within the cards entering the sprint or iteration.
To excel at Just enough and Just in Time requires a level of pre-work before the sprint starts, and honing this pre-work is what a "The Definition of Readiness" is all about.
Quality in; Quality out.