SpaceFN is a concept that uses the spacebar as an additional mod key, see https://geekhack.org/index.php?topic=51069.0
Currently there doesn't appear to be a clean implementation under Linux. As a result implementing this could be a real demonstration of how useful evscript can be. Do you think that is possible?
btw) this doesn't work well when using xcape as xcape lacks rollover detection (see topic I link to above).