Hi Vincent,
We're working on solutions for both of those + collada-dom.
There is a level of granularity that we could consider extending to support blacklisting a specific target/arch pair inside of the build file if we want to keep a specific arch running but not put it into it's own build file.
The one time it might be appropriate to tag something in the package.xml is if the package has binary code included inside which is not compiled but supplied as a blob. However as we strongly discourage those cases and have very few of them, I think that continuing to use the blacklists for them is appropriate.
Tully
PS colladadom and couchdb should be fixed shortly. Some targets are already deployed. (Thanks to Jose for help backporting.) We're still working on openni on ARM. We have versions compiling from source so it shouldn't be too long.