Be able to access all linked elements in custom template report

I'm afraid it could be a major performance issue, or would request a complete refactor of the plugin.
As of today, the plugon works with External Library (TBS) that populates data into the model from stored arrays.
What you request would require to get all data of the project (all activities, all tickets, ...) and store them in arrays to send to the Template.
That could be a very large amount of data (imagine project with hundreds of Activities and thouthands of Tickets), bringing low performance and very high memory comsuption.
Moreover, this would be done evne if the template does not use these extra data (the template is not analyses before retreiving the data)

So no, it is not planned to extend the plugin this way.