Single-letter namespace aliases seem like a bad idea to me. In particular, many of those conflict with something else.

"B:" is already in use for Wikibooks
"M:" is already in use for Meta-Wiki
"V:" is already in use for Wikiversity
"VO:" is already in use for the Volapuk Wiktionary

It is technically possible to override interwiki prefixes with namespaces, but it will probably cause havoc elsewhere and I would expect the sysadmins (which does not include me) to decline to do so. The rest of the task (Add the two new namespaces, add "A:", "H:", and "K:" aliases) is fine and will be done by someone else in due time.

And the above is a two-person discussion. Is the dewiktionary community really so small that two people is sufficient consensus for this scale of change?

(To be clear, I'm not a final decisionmaker here so you don't need to try to convince me of anything, I'm just bringing up some thoughts that others who will actually code this will probably consider)

Well, most people of the german wiktionary community are not interested in technical discussions. So i waited three months before i started this request.
About the single letter namespace aliases:
I once wrote a gadget for enhanced typing in the search field of the wiktionary:
https://de.wiktionary.org/wiki/MediaWiki:Gadget-SearchPrefix.js
https://de.wiktionary.org/wiki/Hilfe:SearchPrefix
You can type "h:" in the searchfield and it will automaticly expand the namespace name. It speeds up typing. But it didn't work on mobile sites because of the overlay thingy that is used there for the searchfield. It only works with vector 2010 skin.
So i thought it would be a good idea to have aliases that will work on mobile and desktop sites. I didn't know that the mentioned prefixes are in use yet.

I think someone would be willing to help with this issue once you get a clear and sufficient consensus, as dewiktionary is not that small.

T363538 means that namespace aliases conflicting with interwikis are now a supported concept.. But I advise against doing so.