I registered just so I can post info on this. I wanted to know same thing as you guys , so I wrote to Gary from FBI - here's just the part relevant to this issue:
"Also , is there any way to know which volumes od Disney collections are you going to release slipcased. I had to trade some of the FB Don Rosa and C.Barks books I had, because those came out later in slipcase sets (I have all 3 so far , not counting Gotfredson volumes which are slipcased from beginning) and I just had to have those
"
and here's Gary's reply :
"All of the Duck books will be slipcased eventually. Since we're not publishing the Carl Barks books in chronological order those cased sets will be coming out at different times. The Rosa books, like the Mickey books, the case will be available with every second book. "
regards...
PS: this conversation with Gary is from october 2014.