The MusicBrainz tagger Picard use such a date format, I like to do the same when using a websource with MusicBrainz. You just can't do manual corrections in the Mp3tag tag panel, if needed, since it's restricted to 4 chars.
Your previous reply strongly implies that it's possible to create this frame in the extended tag dialog. Creating a TXXX frame isn't going to be of any use with applications that support the TDRC frame.
The way Mp3tag displays tags in the extended tag dialog, mapping some field names, not mapping others, and not giving any indication when an id3v2 field is actually a TXXX frame, would make it difficult for most people to realize that they haven't actually created a TDRC frame.
Mp3tag maps the YEAR field to the TDRC frame when using ID3v2.4 (see list of field mappings) and you can enter more than four characters in the YEAR field via the extended tag dialog.