Secondly: sounds much saner doing it on cron.
Thirdly: Yes, to get in any stable release it really needs to maintain backward compatibility with all existing 1.9 and 1.8 mnet installations. So this might mean detecting what sort of version is at the other end and doing things the old way sometimes. As long as you do this then I'll be totally happy to see it going into 1.9.x and 1.8.x.
For Moodle 2.0 it'll be OK to clean out the crufty old code and just implement the newer better methods (there is bit of this already going on in Moodle 2.0 because it's such a major version) but if the cruft is not too big then it might be worth keeping it anyway to maximise compatibility.