Latest update from Affinity support:
"Hi Guy,
We don't have a timeframe to when arrow heads will be added to our Affinity apps at this time. We don't have any mailing lists setup to inform users of fixes. However when we release an update, mail shots are done that include links to the updates release notes, which include information on fixes and features. You can also signup to our support forum and follow the roadmap threads for each app. You'll then receive a notification when a staff member edits this.
Designer roadmap
Photo roadmap
Regards
Lee"
I think I will give up on Affinity creating this facility.