@MarketingUniverse. What you suggested is possible but there are many cons. First you have to create a list for each and every action you want to do. So if its anything in-depth you'll have a bunch of misc lists to handle something that AC does natively, tagging. If it's just to tag someone when joining the site or a handful of other smaller things than yes your suggestion would be fine. The automation would simply be "when joins list add this tag".
Robert G do you know if this has been implemented? I'm searching and no luck at this point. Pretty bummed.