Currently there is no possibility to assign a shortcut to the zoom tool. Additionally, a desirable behaviour would be to use box-zoom tool while holding a key, and going back to the previous tool on key release. Just like pressing "V" to draw lines while using the paintbrush.
Git commit 08427a2b37bbcf9a871fc5eb44561cc7082e0e14 by Boudewijn Rempt. Committed on 25/04/2017 at 13:09. Pushed by rempt into branch 'master'. M +11 -0 krita/krita.action https://commits.kde.org/krita/08427a2b37bbcf9a871fc5eb44561cc7082e0e14