I was thinking about writing an adventure for SRM.
But now, reading the announcement of SR4, I'm starting to think that this 'wireless hacking' may change a lot about how a run would be performed. And then there are all the new game mechanics ...

Is there any use in writing an SRM adventure now, when it may not be compatible with SR4 when it is released?

there sure is! go ahead and write the adventure (well, go ahead and submit the plot/outline to me first of course)...as things become clearer, we can convert it over to SR4. most of a successful adventure is in the story/mission itself, and not dependent on what characters can/can't do - therefore if we have to tweak it for the new "decking" stuff, then we only have to change that. that's not the only big change out there, but probably the one that will affect the adventures the most.