Comment 1 for bug 647214

<Ctrl-q> is taken (exit Inkscape). <Space> is similar to your feature request (switches to the Selector tool temporarily; another Space switches back). On the other hand all tools have single-letter shortcuts - to toggle for example between 'Bezier tool' and 'Node tool', use 'b' and 'n'; or to toggle between 'Spray' and 'Tweak', use 'a' and 'w'.