I don't know that running a google doc precludes the forum. The key benefit is allowing us to do more of the work and updates and not putting it all on Alastair. But we could still post an image of the spreadsheet -- or some corresponding graphic like Alastair has been doing -- here
Put differently, Alastair has been running a spreadsheet privately and posting the results graphically here. I am only suggesting we maintain the spreadsheet collectively but still can post images from it here. Not sure offhand if as nice a graphic as Alastair is doing can be done in Google docs...