I don't know if there is a good *bulletproof* solution for this problem, or not. But there are three different barriers here, one of which is a helpdocs kind of barrier (potential-contributor education), one of which is a technological barrier (ton of work for OTRS volunteers to transition an email-based-comment over to an on-wiki-comment), and the final one that is a legal barrier (copyright release of the email'd paragraphs and privacy concerns w.r.t. the email-metadata such as email-address and email-header-IP-addresses and such).
I suggest attacking all the barriers separately, since lowering any of the 3 main barriers will be helpful to improving the overall situation. First and easiest, why not just improve the helpdocs? The helpdocs which explain how talkpages work, are already good enough probably, but clearly plenty of people don't use talkpages (either they prefer email or they don't wanna learn from the talkpage-helpdocs). So why not improve the helpdocs which explain how to email OTRS? Put a big note, smack dab in the middle of the how-to-contact-OTRS-helpdocs, which says "IF YOU WANNA make a suggestion about article content then please paste THIS EXACT sentence into the top of your email to wikipedia: Dear wikipedia, the textual body-prose of this email, not counting headers and footers which contain personally identifiable information, are explicitly dual-licensed under CC-BY-SA v3 or later as well as GFDL". Modify the phrasing to taste, obviously, but my point should be clear: some people are emailing OTRS about a private matter, but a lot of people are just emailing them about a content-matter. Why not suggest that the person sending an email, *prior* to sending it, add a bit of text which will properly license that body-prose? It would still be up to the OTRS agent whether to *actually* copy the body-prose over into some enWiki talkpage, and they might still need to be careful when doing so to properly elide any email-sigs or email-header-info, but better helpdocs would eliminate some of the hassle (if the person emailing followed the instructions).
Second avenue of attack, why make it more difficult than necessary, for the OTRS folks? It would certainly be possible, using community tech team devs for instance, to whip up a system which would speed up the process of "routing content requests" that happen to arrive via email. First of all, it makes sense to have a gadget which identifies whether a particular email contains the CC-BY-SA release boilerplate (mentioned above), and also a gadget which attempts to automagically-extract just the CC-BY-SA portion (stripping off the email-header and the email-body-sig portions plus inserting a properly wikified OTRS ticket-link at the top to comply with the atribution-required-part of the CC-BY-SA license that the email's body-prose was released under). Then, with a couple of clicks, the OTRS agent will be able to get the properly-licensed properly-anonymized portion of the email, into their clipboard, and can then paste it into an appropriate talkpage. Additional speedups would also be possible, such as having the gadget automatically insert a boilerplate "otrs edit request" header similar to the "semi-protected edit-request" headers used for locked articles, and having the talkpage post auto-watchlisted by the OTRS agent, but those are nice-to-have features.
Finally, methinks there might be some ways to overcome the legal hurdles. Currently there is an OTRS ticket-system. It contains copyrighted emails, which are not meant for publication. Adding the body-prose of such an email, into an enWiki talkpage, would require *re-licensing* the body-prose of that email, under a wikipedia-compatible license. However, I note that it is fine to HYPERLINK from any enWiki page, to copyrighted material hosted elsewhere -- we have plenty of refs in enWiki mainspace (as well as talkspace) which are EL'd unto. It is difficult to explain to a person that is emailing OTRS about a content-matter, that the OTRS agent needs them to "blah blah CC-BY-SA blah blah GFDL blah blah sign here". It would likely be considerably simpler, to simply have a specific domain name such as https://emails.wikimedia.org which contained *copyrighted* body-prose from properly-anonymized emails, that the sender was willing to make public. This obviously ought not be automatic, some emails to OTRS are private. But in cases where the sender was specifically wanting to "make a suggestion to the wikipedia editing community" about a content-matter, is seems likely that they would be happy to have the body-prose of their suggestion displayed on a world-visible website. The downside here is that, if they are making a specific suggestion like "please add sentence1 + sentence2 into articleXyz" it will be essential to get the full CC-BY-SA dual-licensed with GFDL release of that stuff. But many questions are of the form "this seemed incorrect / non-neutral / awkward / etc to me can somebody please fix it?" ...and in those latter sorts of cases, the OTRS agent ought to be able to quickly strip of the headers & footer with personally identifying info (see gadgets in previous paragraph), shove the bodyprose excerpt over the email.wikimedia.org or some similar site (probably still requires permission of the sender of the email -- but is far easier of a request-for-permission to EXPLAIN to them), and then in the talkpage the OTRS agent can link to the OTRS ticket, and for people unable to see the raw ticket, link to the anonymized-but-copyrighted-body-prose over on the separate domain-name.
I recommend fixing the helpdocs first (which is pretty easy and needs no programmers), and then incrementally upgrading the OTRS tools & gadgets second (programmers required), then if-and-only-if-necessary considering the creation of a separate "copyrighted email bodies" domain name (significant obvious downsides but *might* have a practical net upside... try the other options first however). Best, ~~~~
