We agree 100% with the suggestion and are exploring ways to enable this. This represents a significant amount of engineering work hence we don’t have a schedule to share yet.
We’ve rolled out an update which includes support for PDF files, images, audio and other file formats. This update doesn’t yet include support for video files but we’re working on it and will have more to share soon!
We will be adding the ability for administrators to expire external users’ access to entire site collections after a mandatory expiration period, as we discussed at Ignite 2018. That feature will be rolling out in CY19Q3.