In these early days we perhaps spend more time thinking about this question than any other. After speaking with hundreds of news publishers, the truth seems to be that certain topic areas have "staying power" while others are more fleeting. For example, rental price trends, real estate trends, economic data (e.g. unemployment rates), environmental issues (e.g. air quality)are always relevant. The other nuance is that these topics have constantly updating data feeds since the the realities of the world are constantly changing. Kind of like the Pareto principle.