*bump*, because I have a question about this for the Port.
Woomeister, are you sure the reason it doesn't work is the sexp limit? Because I can't imagine that the limit would be different for FRED than for FS2.
We have a particularly large mission for the Port that has completely maxed out the retail FRED sexp limit. We want to add another sexp or three, but we can't without exceeding the limits. However, if we can use a specially-built version of FS2_O that'll handle increased sexp limits, while still allowing people to play it on retail FS2, we'll jump on it.