Here's a few features I noticed were missing from the Trajectories Addon when I was testing PR #2220.
These shouldn't delay merging PR #2220 because that PR is desperately needed to make the Trajectories Addon work at all. But they shouldn't be forgotten either, so I'm making this a separate issue to correct after PR #2220 is merged:

• Once Addons:TR:SETTARGET() has been called, there's no way to actually un-set the target from the script. (Also no way for the script to un-set it after the user manually set it).
• A script cannot query what the Trajectories target is currently set to. It can query that the target exists, but not what it is. There should be a way to obtain the GEOPOSITION from it.
• The manual GUI interface lets a user pick a descent profile that is neither prograde nor retrograde, but something in between, with the sliders. There is no way for a script to do this right now. Perhaps making a script able to set/get the value of the 4 variables attached to those slider values would help.