That would be a pretty complex hack. Here are the potential problems that I see without trying to make it work:

#1: obect_tasks is NOT designed and tested in situations when there are multiple instances of helper called on the same page. If you noticed, there is only one subtasks block per page in the system. It might work flawlessly in multi-instance situation, but you may have big problems also.

#2: You would need to have mass edit form outside of the tickets table, not around it. On submit you should collect values from checkboxes, create a request with proper POST values and submit it. In this case you would also lose a lot of simplifications checkboxes() helper offers (a small jQuery helper that we developed to help us make massedit forms more usable) and implement all the functionality on your own.

#3: If you have a lot of tickets on the page with a lot of tasks, assignments etc you might end up with one page that takes a lot of space, resources and is really slow to generate. We have 200+ active tickets and 100 of them have subtasks (about 5 in average). Type of display that you are proposing would never work properly in that situation.

You would need someone with a really good understanding of JS and jQuery to make everything work and have everything covered.

Objects listed on milestone details page are collected through on_milestone_objects event. activeCollab does not know in front what types are related to milestones so it needs to "ask" plugins to return objects by triggering that event.

Result is forwarded to template as $milestone_objects variable where key is section name and value is array of objects that need to be listed. Basically, you would need following code in foreach that loops through $milestone_objects to see if objects you are working with are tickets:

{if $section_name == 'Tickets'}
  ...
{/if}

Same notes I posted in previous post apply here. Use at your own risk.

If you want to be able to use object_tasks helper you'd need to render tickets section on your own, now use list_objects helper. Something like this:

{if $section_name == 'Tickets'}  
  <table>
  {foreach from=$objects item=ticket}
    <tr>
      <td>#{$ticket->getTicketId()}</td>
      <td>{object_link object=$ticket}</td>
    </tr>
  {/foreach}
  </table>
  {list_objects objects=$objects show_checkboxes=yes show_header=yes}  
{else}  
   {list_objects objects=$objects show_checkboxes=no show_header=no}  
{/if}

You can put anything you like in the ticket listing this way, including object_tasks call. Please note that you'll probably need to style it with some CSS.