there is an option "fire towards enemy" for badgers. As this already exist it would be very handy to assign this also to firewalkers and merlins.
If a user enable this for 1-2 of his firewalkers he could create a death zone for cloaked units.
Otherwise he has every time to set manual fire zones which break on movements.
This option would be cool to remove some micro and let the player focus more on macro.