Just about everything can be executed asynchronously in Yummy FTP - it's not down to the protocol itself, since this is entirely synchronous, but since Yummy uses several connections at once it can use those resources to perform many tasks at once, calculating folder sizes included. If, however, a server is limited to only allowing one connection at a time then this automatic folder size calculation would block any other actions until completed - not what you want.
There's no technical reason why this capability couldn't be added, but certainly, a preference would be in order if this automatic behavior is something that others would like also. Votes please!
