Earlier quoted context omitted.
> - Don't bundle third-party dependencies. For security (and for better documentation of the true dependency graph) distros often must go through extra trouble to unbundle third-party libraries when present. Some project even add their own custom patches to their bundled source. Resist the urge to do this. If any of the dependencies aren't currently packaged in Debian, how would one follow this guideline?
In addition to what rleigh said, you could package them for Debian :) https://mentors.debian.net/intro-maintainers
If I wanted to package my third-party dependency, the first thing I would do is "learn about personal interests of sponsors" and see if my third-party dependency and a sponsor's interests intersect. There's a link to a page describing the sponsoring process, where apparently I'd file a bug against a "sponsorship-requests" pseudo-package and then, I guess, wait.
Next (or perhaps concurrently) I'd file a separate "Intent to package" bug against the "Work-Needing and Prospective Packages" pseudo-package. There's a whole page about WNPP and format guidelines for submitting said bug using the "reportbug" tool. Those format guidelines are longer than the JSON spec.
Then I'd still need to make the package, after all. That link you gave lists five important reference materials, one of which is said to be "must read" and has 12 chapters and 7 appendices. There's also a "New Maintainer's Guide".
Then I need to publish my package. There's an account to sign up for. Plus I'll need to create, keep up with and sign stuff with a GPG key because uploads are http/ftp only.
Once that is finished I apparently get an email response. Finally... I am done!
Now it's time to find a sponsor.
There's a whole section on what to do if you can't find a sponsor. The first is to follow up on the WNPP request I was supposed to make six paragraphs ago. The other is apparently to look up sponsors in a sponsor search-engine on the Debian website and bother them.
Then there's another section on actually getting the package into debian through an ftpmaster. (Both the sponsor and the non-Debian Debian-package maintainer are ominously reminded here that the ftpmaster's _opinion_ on inclusion is binding.)
And then maintaining it.
I would be, for the life-time of my application, maintaining the Debian package of one of my third-party dependencies. This, in response to my query about how to be a good upstream citizen in the hopes that downstream maintainers can more easily package my application! :)