Shouldn't we be engaging with the Memento community as well about something like this?

That's a really good idea. I'll send a question to their dev list.

Yeah, @hvdsomp is very responsive and I guarantee you'll get some good discussion.

Thanks for the ping, @ajs6f and @acoburn! I am replying on behalf of @hvdsomp and other members of the Memento crew.

Suppressing the optional "from" and "until" parameters in a timemap link is definitely a pragmatic solution but one that comes with the loss of relevant information - the time span covered in the timemap.
The preferable solution, in our opinion, is to use/promote the use of HTTP link header parsers that do "the right thing", meaning the recognition of commas in headers and their recognition in context. This would likely also help for parsing other headers that hold a datetime such as Memento datetime, Last-Modified, and Date. From our experience, the popular Python-based "requests" library is a good example for a library that distinguishes between commas to separate link headers and commas used within quotes (like for the Memento datetime). For the following link header:

Link: https://github.com/leeper/pdfcount; rel="original", https://scholarlyorphans.org/memento/https://github.com/leeper/pdfcount; rel="timegate", https://scholarlyorphans.org/memento/timemap/link/https://github.com/leeper/pdfcount; rel="timemap"; type="application/link-format", https://scholarlyorphans.org/memento/20180828012815/https://github.com/leeper/pdfcount; rel="memento"; datetime="Tue, 28 Aug 2018 01:28:15 GMT"; collection="memento"

the parsed and formatted output is:
{
'original': {'url': 'https://github.com/leeper/pdfcount', 'rel': 'original'},
'timegate': {'url': 'https://scholarlyorphans.org/memento/https://github.com/leeper/pdfcount', 'rel': 'timegate'},
'timemap': {'url': 'https://scholarlyorphans.org/memento/timemap/link/https://github.com/leeper/pdfcount', 'rel': 'timemap', 'type': 'application/link-format'},
'memento': {'url': 'https://scholarlyorphans.org/memento/20180828012815/https://github.com/leeper/pdfcount', 'rel': 'memento', 'datetime': 'Tue, 28 Aug 2018 01:28:15 GMT', 'collection': 'memento'}
}

and for the link header with from and until parameters:

Link: http://a.example.org/; rel="original timegate", http://a.example.org/?version=all&style=timemap ; rel="timemap"; type="application/link-format" ; from="Tue, 15 Sep 2000 11:28:26 GMT" ; until="Wed, 20 Jan 2010 09:34:33 GMT"

it outputs:
{
'original timegate': {'url': 'http://a.example.org/', 'rel': 'original timegate'},
'timemap': {'url': 'http://a.example.org/?version=all&style=timemap', 'rel': 'timemap', 'type': 'application/link-format', 'from': 'Tue, 15 Sep 2000 11:28:26 GMT', 'until': 'Wed, 20 Jan 2010 09:34:33 GMT'}
}

We are not aware of any many Java-based libraries that perform equally well. We developed our own Java-based library to correctly parse headers and we are happy to share the code base. Our implementation in based on input from here:
https://jar-download.com/artifacts/org.jboss.resteasy.mobile/resteasy-mobile/1.0.0/source-code/org/jboss/resteasy/plugins/delegates/LinkHeaderDelegate.java

Another example of a project that adopted the same code base to implement a link header parser is:
https://github.com/temenostech/IRIS/blob/master/interaction-core/src/main/java/com/temenos/interaction/core/hypermedia/LinkHeaderDelegate.java

Regardless, we would be interested in seeing our custom implementation integrated into off-the-shelf Java parsers - can you see a collaborative path to make this happen?