No, I mean in general it is already possible to put "Cancer 3" somewhere, but you can't easily put "Whatever ship is occupying the 3rd slot in Cancer wing for the current wave". But then I had an idea for how to make a sexp like this:
(not yet implemented)
op member-of-wing
Cancer
3
which would be equivalent to "Whatever ship is occupying the 3rd slot in Cancer wing for the current wave". It might also be useful, if it isn't implemented yet, to have a sexp to query what wave a multi-wave wing is on. Possibly like this:
op wing-latest-wave
Cancer
which would return the number that the specified wing is currently up to, as far as waves (and the value it returns would increase every time the next wave arrives. It probably would start at zero up until the first wave arrived. Finally, it might also be necessary to have something like this:
op has-wave-arrived-delay
Cancer
2
10
where the 2 is the wave number and the 10 is the delay. This would be so that, in addition to being able to check what wave you're at, you could also use changes in that as cues for events.
Of course, if there's already an easy way to do it, this would be unnecessary (but might still make things more convenient, depending what it takes to do these things now).
Basically, it's a "sexp request"