Hello,
if you are interested in getting an insight into the decision of removing the IDL compiler from the user-land tool chain (in both Genode and L4re), you may refer to my study of the subject:
"A Case Study on the Cost and Benefit of Dynamic RPC Marshalling for Low-Level System Components"
http://genode-labs.com/publications/dynrpc-2007.pdf
As far as I know, the integration with Ada would actually be quite straight forward because the class layout of Ada is compatible with C++. This enables you to call virtual C++ functions (the IPC stub code) from Ada code.
Regards Norman