Ahh. Hit the wrong key. Hope this aint sent twice
We in ATC have been using conditional clearances for a long time. We give a conditional clearance, the pilot is required to read that conditional clearance back, and we are required to get the conditional clearance readback!!
I really dont think adding an extra BEHIND to all that is gonna make a difference. The pilot understands or he/she dont. There are enough BEHINDs in aviation and Airservices as it is
When we use WAIT with a line up clearance, it can be used with less-than-perfect-english-speaking-pilots, but also used to more-perfect-english-speaking-pilots, and normally indicates you aint getting a rolling start, so if ya have back-tracked, dont spool up as ya spinning around at the end. Ya aint goin anywhere :-)