Its honestly ridiculous this tool isn’t better. WordPress is 25% of the web. Its Open Source. The tools to make this happen already exist. There is literally no excuse not to execute.
The problem is featured image XML data isn’t included in export XML files, correct? Except that it IS included if you export everything, instead of just posts. Hubspot still doesn’t import that data, so its really not a WordPress problem. Second, there are specific tools and plugins to export JUST the featured image XML, but Hubspot doesn’t recognize those either.
Lastly, lets not forget how structured data is going to change dramatically this year coming out of WordPress because of Gutenberg, meaning you’d have to address this anyways, meaning its downright malpractice not to do so in a meaningful way, which is to include featured image import.
If you need help with resources in the WP community to make this happen, I will gladly do so.