Prototype solution to prevent caching of Wagtail previews - https://github.com/wagtail/wagtail/issues/5074

home_page.html

{# home/templates/home/home_page.html #}
{# Uses safecache instead of cache to prevent caching of preview content #}
{% load safecache %}

{# Usage of cache tag remains the same #}
{% cache 3600 homepage_charfield %}
  {{ self.a_charfield }}
{% endcache %}

safecache.py

# home/templatetags/safecache.py
from django.template import Library
from django.templatetags.cache import CacheNode, do_cache


register = Library()


class CacheIfNotPreviewNode(CacheNode):
    def __init__(self, wrapped):
        self.wrapped = wrapped

    def render(self, context):
        if context['request'].is_preview:
            return self.wrapped.nodelist.render(context)
        else:
            return self.wrapped.render(context)


@register.tag('cache')
def cache_if_not_preview(parser, token):
    return CacheIfNotPreviewNode(do_cache(parser, token))