@LincMitch this worked for me to solve this issue:
import React from 'react'
import remark from 'remark'
import remarkHTML from 'remark-html'
const toHTML = value => remark()
.use(remarkHTML)
.processSync(value)
.toString()
const YourPreviewTemplate({ entry, getAsset }) => {
const asMarkdown = entry.getIn(['data', 'something'])
const asHTML = toHTML(asMarkdown)
// ... etc etc ...
}