...adding a new card would be difficult and open the possibility of worse bugs resulting from interactions between the authors codes...
^This is the crux of the issue with card creation. Balancing is a tricky and time consuming thing to do.
Not that it will ever happen but......
If we were to implement a community driven system I would argue for a reboot of the entire crucible, forge & armory. I bet if people knew cards had an actual chance to get into the game the submissions would improve.
Unless there is a revolutionary superior system it would probably reboot only the Crucible and add a new layer. I do expect most ideas would get more fine tuned. (The problem is most of the card creators think their submissions are great)
Thorough discussion and analysis at the low end can help. To some extent this happens already. What is missing is a means of quality testing at the higher end...
This means, in my opinion, the community needs to get more involved in play testing at the forge level and higher.
The discussion based sifting / feedback works well at the low end for spotting obvious issues, but true balance and quality control takes play testing.
Without data and feedback from play testing, higher levels of card creation voting will just be more rounds of popularity contests.
So what would be good here is
1) Some form of play testing standard (we have a simulator, so thats perhaps a place to start)
-This likely will take playing many, many games to get a good feel for a card so there will need to be a way to get lots of community
members involved.
2) A place in the forge (or maybe a new area altogether) to record play testing data and feedback
-Without some kind of quantifiable data to base voting off of, the polls will just end up measuring personal opinions.
(cost theory, etc. are good, but really there is no substitute for play testing)
Once quality testing of cards can be sufficiently improved, then we can think about increasing the frequency of updates. Otherwise we will be in for a nightmare of balancing issues.