It's tricky to get html import right, both because the html we use in the web world and the one in emails is not quite the same (email html is stuck 10 years in the past)
so going full html is probably not going to happen without significant investments, but you mentioned the issue of a single long line.
This one is probably easier to handle in a safe and satisfying way. Do you, or does someone in your team have some dev skills? it wouldn't be too hard to alter the display or the processing to inject
where they are new lines.