I don't see anything blocking you from passing in the array (with one element if there is only one) and using a Template loop.

Paraphrasing Tolstoy, all template-conforming fields are alike; each non-template-conforming field is different in its own way. One example I had provided involves multiple inputs per field; another might have a bunch of specialised CSS classes or require a small piece of JavaScript attached to it to provide necessary interactivity where available, and so on. If I try to write a template general enough to tend to all of them, it would be a mess, I expect. On the other hand, storing pieces of Template code (i.e. providing specialised mini-templates for non-standard fields) in the form description seems against interface/behaviour separation.