OK look, I can made a level within a day or two by using keengine and convert it into a png. I only need some free time. Later, if you wish, you can try remaking it with Abiathar. Or even better: if Abiathar could import PNG's and convert them into levels? I'm not sure that's possible. But the problem is that this will require a lot of testing the design and I fear that most of the things I would make in KEENGINE would not work the way I think they will in Keen 6. Or I would like to make something and testing it first before making a level out of it. And if I'm not able to test all the things, it won't be the level I would aim for. And not to mention that there are also memory limitations (such as the number of pick-ups you can collect per level , zappers disappearing if they're too much etc.) which I'm really not a fan of. And lastly, the trick shorts I have in mind would work only with GOD mode anyways (and probably would not work at all) and would require countless attempts in order to make them anyway.
Here's my first idea for the testing grounds: You begin in the world map similarly as in Keen 6 and right at the beginning you will be able to choose between 3 ways. Each way will represent levels with different difficulty. For example, the left way would be with easy levels. These levels would require making regular jumps, pogo jumps and impossible pogo jumps. Also maybe door and switch puzzles. Medium levels (the central way) would require some skills by using the impossible pogo and impossible bullet riding. The hard levels would be the insanely designed levels which would require all the known glitches in order to proceed (including such as death, saving, loading for exiting, zapper bullets riding etc.). Also, I would suggest making a patch for an "ankh" pick-up that will give you invincibility for these levels.
The aim of each level would be to collect medals: bronze, silver and gold. Only one medal per level before exit. In easy levels you can find bronze medals, in medum - silver, and In hard - gold. Or, maybe all three medals per level, but depending on which way to make it. Passing a level and you advance further, but there also should be a patch for making these levels re-enter able, even if they are finished. So for example, if you took a bronze medal in one level, be able to play it again and aim for silver or gold medals.
Here are some medals:
And here's a one hour, medium difficulty level: