Lots of good suggestions there. You might be interested to know that the list of improvements/modifications is something like 700 ideas long The development is a long ways from stagnant, and many of the things which you addressed are in the works.
Part of the concern is the KISS principle. It is relatively easy to throw in hundreds of additional settings, but this could cause incidental increases in complexity for all users, some who struggle with what is there now. Perhaps an "Ultra-expert" version will have to eventually be made, who knows?
Re: #9 You can place a "point along entity" to extend a line. Use a negative value to make the point move off the end of the line.
Like I said, I have no argument with your other ideas, and I know that addressing some of them is in the works. Some involve a lot of complex programming to accomplish, and have likely not been done yet just because of priority.