Sorry for the previous curt reply, as I'm pinned down for time and am having a hard time doing what needs to be done and not explaining fully why or why not a feature request is feasible.
I'm not stuck on whether or not it *can* be done, as it would require about three lines of code using what's already in VA. The issue is whether it *should* be done, as my take on 'globally'-effective functions is that it's always great right up until you don't want it to be. Where this squirrels off is when ALL input is blocked and then the user is effectively hosed... they can't use the keyboard or the mouse to do anything and will probably need to just power down. So then it becomes a customizable feature on what keys/mouse buttons are blocked and not blocked. That's a lot of UI for new request that's only been asked for once, so, in lieu of saying, 'This will take a long time IF the demand is there', the suggestion was offered. The onus is on the user, and yes, it will require a command for each and every key/mouse button you want to block, but it can be done now.
Also, you can create an Autohotkey script and call it from VA.