It would not be open sourced immediately when SE5 is released. And besides, SE5 will be fundamentally different that SE4, just like SE4 was different from SE3. You couldn't really take the source code of SE3 and build SE4 out of it. You would not be able to do the same with making SE5 out of SE4.
Well... not without rewriting everything, and essentially writing a new game from scratch.
[ January 27, 2003, 00:10: Message edited by: Imperator Fyron ]