I am running a online game of Dwimmermount at the moment and am very interested in finding out whether any additional preview levels are going to be made available to kickstarter backers?
Yes, James is working on fleshing out his notes for level 3A and 4, and then going back to do 2B and 3B. Each level will be released to backers as a draft as it's completed.
We'll also be posting James' original notes from the levels, which provide a fascinating perspective on the evolution from DM notes to text written for others to use. The Level 1 notes are now up at the download page linked to in backer Update #4, I will also post its info in the Dwimmermount backers-only area and send it again as a new update.