I'll note the biggest gotcha I can see here to let people comment on the desired interaction where the "next steps" don't align.

One catch and reason the (admin) user is currently prompted to process each decision or activity is that they each could theoretically have different finish actions.

So a "Review" task might have options to "Decline" or "Accept" whereas another task might have some or entirely different Next Activities.

In terms of solutions and interaction, I could imagine some options:

1. When performing a "bulk" action, the user could select from ALL the possible options from all the selected items in one go (thought this seems like an odd interaction).
2. Users can only perform bulk actions by selecting everything using the same task. User can't select everything and act on the entire list unless the tasks are all selected. Maybe an option to choose like tasks would help.
3. Workflow introduces a new concept or way to define "Accept" or "Decline" a task so there could be a single "accept" or "decline" all button?
4. Perhaps there shouldn't be an "accept all" button. But rather the full list should let users try to set the next activity across multiple items in fewer clicks?

As an idea, I want to be careful to not suggest the ultimate solution but a change here will need to address a list of tasks with different next steps.

This is exactly what we have been looking for. We wanted to have translation job name, page and target language associated with the items in the list to filter, search, sort, approve/reject, etc.

Nick - this exactly. As an admin user, even when selecting 'Finish All' you still have to individually Finish each of the multi-selected workflows. This is a multi step process and still requires users to select each Next Activity stage, thus not saving time when the user already knows what next stage they want to finish the content in. It would be helpful if "Finish All' resulted in actually Finishing All selected to the target. 

For admin users, in the Classic UI, we already support the Finish action on multiple activities:

However, where a next activity (and optional message) is required, the user will need to be supply this separately for each selected activity.

So, what's being requested is a similar list to this, but for a normal (non-admin) user's activities, which they can filter, search, sort, etc., and which would have an 'Approve' action. Pressing 'Approve' would allow the user to provide a single message and 'next activity' (e.g. 'Accept'), which would then be used to finish all the selected activities? And probably the activities in the list should provide a clearer indication of the item(s) with which they are associated?

Yes I think that sums it up. The process of approving one component at a time in the activities tab takes more effort that it needs to, in cases where the reviewer knows the context and knows that several separate items are ready to go and can be approved using a single action.