One of the frustrations of publishing Master Templates from Motion 4 to FCP7 was the fact that dropzones and text entry/tracking were the only controls that transferred between the apps. With Motion 5 and FCPX that's all changed, welcome to rig building.
The link between FCP and Motion had to grow stronger, the problem was that they were two different apps, one very old and written in Carbon, the other a lot newer and written in Cocoa from day one. Two development teams too. They were software neighbours, but could only chat briefly over the garden fence. With the release of the new versions of the apps that's all changed, they've got married! You now can write an effect, generator, transition or title in Motion and publish the parameters via rigging so that it can be animated in FCPX.
GeniusDV have put together a great tutorial on how to build a rig in Motion 5 for a particle emitter to be used in FCPX. We think once editors get familiar with this new feature it will make the generation and repetition of complex effects and transitions really easy. Or in another words, do all the cutting in FCPX, do all the complex effects in Motion, flip between the two with ease.
GeniusDv have also posted the Motion file as an example to help.