I’m not sure what is going on with 0.7.5. Either there is a bug and the feature was not fully enabled, or the changelog is slightly misleading because the release only includes the internal compiler support, with the matching base library exposing the feature to follow in the next release.
@ggreif would know the answer but might be on holiday still.
I’ll try to investigate tomorrow.
If you are using dfx to build the sources, you may still need to tell dfx to actually use moc 0.7.5 using environment variable DFX_MOC_PATH (or similar, I may be misremembering the name)