Workflow actions that can update properties across different (associated) object types.
Our company uses your workflows HEAVILY, but we are constantly having to work around one major limitation: The workflows can only change properties on one type of HubSpot object. For example, if you start a ticket-based workflow, you can only change a ticket property. But there are often contacts, company records, and even deals that are associated with that ticket, and it would be extremely useful to us if we could update properties on those associated records right from the same workflow. Something that happens in a ticket, for example, OFTEN impacts a property that "lives" on the contact record, or company record, but we can't even trigger a workflow on that other record, let alone update the property.
We understand this is probably a challenging thing to accomplish because it would likely require the workflows to have the ability to perform a relational query in order to cross-reference and update different objects. But without this capability, we often find that we have to rely heavily on our developer to go the last mile (using APIs and other custom software) - just to make two related things in your database "talk" to each other.
The other option we currently use to accomplish what we need to do is use your reporting tool, which does at least let us run reports on two item types. With this tool, we have to build a report that helps us find the records that have gotten out of sync (because they couldn't update automatically), and then go to the records and update them manually.
Asking our sales team to update lots of properties manually doesn't help me sell the benefit of HubSpot to that team - I've received feedback from them that it just makes their interactions with HubSpot feel like busywork.