Hi @anon23458333,
When you say “on kanban cards” what do you mean? On the card when it’s on the border? In the detail view panel on the right side of the board?
I wouldn’t recommend a custom field unless you’re building the app for personal use only – it’s not possible to programmatically create custom fields via Atlassian Connect.
A web panel on the view issue page is probably the most flexible option for you to completely customize how your data looks, since it provides an iframe. These are not going to be visible on the card itself, but they are visible in the right side detail panel with the atl.gh.issue.details.tab location. The right hand side panel will be replaced in the future by the new Jira issue view and the glances that you mentioned.
Wiki renderer is not available in Cloud. Another option is to use an Issue Field, but only plain text is supported.
I don’t think exactly what you seem to want to accomplish is currently possible, but hopefully this helps point you in the right direction.