Ignition already has drag and drop for tags into the 'Tag History' on data property binding. As well as the drag and drop on the easy charts. Why can't we use this functionality from the tag tree browser to a new version of the power table with a date range? You could also utilize the sample size interval setting within the tag history property binding. This way we could have some built in functionality to look at the history of strings along with all other datatypes.
It may not be built in but it should be possible with indirection and scripting. The easy chart is meant to be easy, nobody said the Power Table was easy 
- User selection of tags in the Tag Browse Tree populates the "Selected Paths" property
- Assuming the user has clicked their tags, if they are "dragging" onto the table you could use the
mouseEnteredevent on the Power Table scripts - In the script update a custom property, that is storing the tag paths used in the the Power Table's binding, you would bind the data using Tag History and indirect parameters
- Easiest with 1 tag at a time since the tree component can be set to only select 1 tag
I was able to find a way around it with almost that exact process. I was just trying to point out that almost all of the functionality is there already. Why not set a a different kind of table to have it built in. Just trying to get the idea out there. Especially since there is no built in way to review historical string tags.