the new tabs would pretty-print the xml or json data for easier viewing
Those of us that have been around a while know that TOAD formerly used to nicely support XML and this was expressly removed in 9.8 (?) for reasons related to bugs in the OCI. Have those bugs gone away? I think the TOAD devs made the business decision to just not support this kind of thing. So TOAD doesn't do natively XML, JSON or SDO_GEOMETRY for example. Are you asking for read only or read/write in this idea?
Also there just is the matter that often the value is just too big to read in a GUI. There is that other product that does read, parse and display these big objects and I dislike it as its hard not to accidentally view a value that is massive in size (like a polygon with 200,000 vertices). What happens then is it all locks up while it grinds away bringing across the 400,000 numbers that make up the polygon. Clearly some TLC could work around the issue showing a limited preview perhaps and only fetching the whole object if the user really, really, REALLY wanted it. That other product has gotten better at that kind of thing but a preview that more adequately warns me "for god's sake don't try to view this in a gui" would be swell.
Actually, the bugs in the OCI haven't gone away. Unfortunately, they only exist when you have the unicode flag set and when we made the decision to support unicode, we inherited this issue and there's not much we can do about it for XML. For JSON, in Oracle, it's simply a CLOB or Varchar2 so it gets a little tricky to how you support it since there is no native JSON data type.