Welcome to the Speckle community, @allisterlewis. It’s great to see you here. Introduce yourself if you wish, we’re happy for you to promote ADDD while you are at it 
ArchiCAD 27 support will be introduced as part of our 2.18 release, which we are moments away from publishing as a Release Candidate. You can get early access to our WIP builds within Speckle Manager using the flag:
Give that a whirl, let us know how it goes, and keep your eyes peeled for the official 2.18 release announcement.