I am experimenting with using Omnivore (an open source read it later platform) with DT and so far I am really like the ability to import from Omnivore (via Obsidian) with my highlights intact. Omnivore is a better interface than DT for reading/highlighting and with DT I am able to permanently preserve my highlights.
For those interested, here is the article explaining how to connect Obsidian to Omnivore: https://docs.omnivore.app/integrations/obsidian.html#scheduled-sync. From there you just need to index the particular Obsidian folder.
In my case, I am using the following syntax:
# {{{title}}}
{{{content}}}
---
{{#highlights.length}}
## Highlights
{{#highlights}}
> {{{text}}} {{#labels}} #{{name}} {{/labels}}
{{#note}}
{{{note}}}
{{/note}}
{{/highlights}}
{{/highlights.length}}
{{#fileAttachment}}
---
![[{{{fileAttachment}}}]]
{{/fileAttachment}}
This pulls in the full text of the article with highlights intact. And brings the highlights as separate text at the bottom of the file. It does not work well with pdfs, because I cannot get it to actually embed the file in DT the way it does in Obsidian, but it is workable.
Just putting this out there for anyone interested.