I agree a MM would be good.....the owner of Nimble is discussing doing one.I have played once, and next week is a second session as a player (a Cheat). I really enjoyed it. I would try to get my main group to switch from 5e to this, but that might be hard to do. Also, and this is big, there's no official VTT support, so all of those thousands of 5e monsters I have are useless. Nimble needs a monster manual to drop online. I started to prep Sunless Citadel to convert to Nimble.
.the dev dropping out of the vtt support really hurt.