I wonder if it is possible to add some of these enhancements to the main Lazarus code tree.
I would love to see that. It would not only follow the rules of our license but also its fundamental idea.
GPL was created so that code can be copied and modified with no shame and then published for others to copy from.
I personally backported one feature from CodeTyphon IDE to Lazarus some years ago. It was the small button at the end of component palette which opens a list of all pages. It becomes very handy when you install a few extra packages, for example Indy.
The feature was modified and improved after copying. It is not true that CodeTyphon's code is always superior, actually it was dummy and hardcoded to some package names. That's not the point however, code is always improved incrementally. Using the full potential of FOSS development would improve code for sure.
I think no other features have been backported.
If you have some cool feature or bug fix in mind, please port it to Lazarus and create a patch.