Do you mean that you want to have these tags visible in the library?
At this time only key and bar are missing. Adding field to the library however requires updating the related SQL file, preventing it to be read from older versions, so I think I'll wait the v3 to do this.
Do you mean the ability to save these tags in the MIDI file?
Song Title, Artist are already here.
Key may be implemented once available in the library.
Time and bar length have no corresponding meta events to encode them.