Did you then shutdown and restart the server?  We've tried this on multiple servers and multiple AEM versions now and the behavior is the same.  The initial sling:vanityPath setting works, but after a restart it no longer does.  Also it works for pages, just not assets.  It looks like the Resource R...

I'm manually creating vanity URLs on assets by setting the sling:vanityPath parameter under the asset's content node. This works fine for pages, and initially is working great for dam assets, but after rebooting the assets are no longer available under the vanity URLs and return a 404. Is there some...

No.  One glaring piece of functionality currently missing is design mode.  You must switch to classic UI to use it.  Components that require multiple images or multiple rich text fields are also not working under touchUI.