Creating strings of driver commands is like writing computer programming code. I don't know of any language that does not permit copy/paste or search. I don't know of any programming language that does not allow a printout of the entered code. I don't know of any language that lets you see only about 20 instructions at once.
While I take your point, in my researches for several technical works I have come across a number of "programming languages" that fit your descriptions above - mostly in the multimedia, graphics and gaming areas.
With Trainz driver commands the "programming", as it was originally created, was totally linear and this works well within the confines of the "game" and the requirements of the vast majority of users. Some users with more advanced needs, such as trev999, have created driver commands that add branching capabilities ("Jump to Label", etc) that were never intended by the original game designers. I have come across very few sessions that make use of these more advanced driver commands.
The question will ultimately come down to one of "useability" vs "complexity". I have created some very complex sessions in the Session Editor (where cut, copy and paste are available) but the idea of printing them out would serve no useful purpose and would be a waste of effort and paper. Ditto Driver Commands.
The current system of "programming", and I include the Session Editor and Session Rules in that definition of "programming", certainly has its limitations, but it is no different from other "multimedia/gaming" user languages that I have come across. In my view, it still meets the needs of the vast majority of Trainz users. Certainly there will be users who are very experienced at using modern procedural and event driven languages who could be very creative and productive if such capabilities were available in Trainz driver commands and the Session Editor. In those cases, the features you are requesting would be of some advantage, but I would put this well down the list of priorities for N3V.
Perhaps we may see some incremental developments in this area.
My thoughts.