I'd like to propose a schema for a redirect system for all Mediawiki sites for improved QR code compatibility. My proposal has several parts.
Version 1 is the simplest QR code variant with 21x21 ROWxCOL's. With high error correction this allows a total of 17 (30% correction)/27 (25% correction) alpha-numeric characters (0 to 9, A to Z,
space, $ % * + - . / :). Version 2 25x25 with 34 (30% correction)/48 (25% correction).
Article titles can be light years long so a shorter redirect would be helpful. However even something as simple as http://r.wikimedia.org/ has 13 characters to begin with. I don't know if enwp.org is under WMF control but http://r.enwp.org/ would be 18 characters. The remaining characters would be used for the redirect itself.
Each page on wikis have a page ID, a decimal value. However these on some wikis can get fairly large. En.wp has 40,592,460 pages for example. This can however be expressed in base 36 since QR codes will have to be alpha-numeric anyways. So instead of 8 base 10 digits same number would be expressed with 5 base 36 digits (O61CC).
Furthermore with an encoding of something like PLLCCCCCC 9 characters would be enough to determine the Project (Wikipedia, Wikinews, Wikisource, etc - 36 total projects), Language (en, fr, es, ru, etc - 36 * 36 = 1296 languages), Code-word for Article ID (36^6=2,176,782,336 possible IDs).
So... Possibly with http://r.enwp.org/PLLCCCCCC 27 characters would fit 25% correction version 1 scheme.
Once this is implemented perhaps WMUK's QRpedia may be easier to implement.
This relates to: https://www.wikidata.org/wiki/Wikidata:Project_chat#Article_specific_QR_codes
I realize the above link may become obsolete with archiving... :p