Marked 2 has been fixed up for Yosemite. The working version is available immediately for non-Mac App Store customers through download and automatic update. MAS users will have to wait for the App Store stamp of approval to be granted, and based on recent turnaround times that may be a week or more. It’s coming, though.
This is a companion discussion topic for the original entry at https://brettterpstra.com/2014/10/21/marked-2-and-yosemite