Remember folks, in Marketo you can build an easy solution for this in about 3 minutes.
You simply create two fields and one workflow that simply appends field #2 to the master field 1 after every update. That easy. The key reason you can do this in Marketo, and not in Hubspot, is that this requires the ability to reference field tokens in workflows, but Hubspot only built field tokens to be available in email writing, and never made them referenceable in workflows (e.g. imagine a workflow that says when field Company is changed, update text field Job Title to equal “{{Job Title}} - {{Company}}”. Hubspot will allow you to type in a value here, but not to reference another system field).
Edit: Nice detail added by the user below me. Field references in workflows are available in Hubspot (as long as you reference the same object only), which allows us to append data to fields, by building the workflow described below. Thank you.