“Many garden railroader desire for many years a decoupler, which can easily be replaced by the current standard coupler.” – Massoth.
As an “Autumn Special”, Massoth introduced an automatic uncoupler which is compatible with standard hook and loop couplers.

The revolutionary decoupler (Art. 8414002) has an integrated motor that pulls down the hook, and simultaneously a part of the loop is being pushed forward to release the hook from the other car. The coupler needs to be wired to a function output of a decoder. Depending on which locomotive you will be installing the coupler on, you might have to modify the coupler shaft to make it fit.
A video by Massoth showing the coupler in action: http://www.massoth.com/en/produkte/8414002.en.php
[Update] Massoth released the English manual, which contains a table showing the compatibility of the Uncoupler with various locomotives of several manufacturers. Link: http://gscalenews.com/pdf/massoth/84140xx.pdf
Introductory price until 31/10/2012: €79 for a set of two couplers.