Are there any plans in the future to rework Moodle to use/implement NOSQL databases?
I haven't heard of anyone planning this but Moodle relies pretty heavily on the use of SQL - so it would be quite a significant task... can you give any examples of large open-source software packages that support both SQL and NoSQL databases on the back end? (I'd be interested to see how they manage it)
..of course many of Moodles db calls are abstracted into functions that could be handled by a nosql driver like get_records/update_record/insert_record calls - but the more complex areas that use sql like enrolments/roles/reports all make heavy use of SQL that may not be easily portable to NoSQL
I think Drupal can take advantage on NoSQL.
http://drupal.stackexchange.com/questions/991/nosql-vs-other-sql-drupal-setups
I'm interested for the reason behind your question, do you have something specific in mind that would require a NoSQL database?
As Dan describes, NoSQL databases aren't just drop-in replacements for SQL databases, so it wouldn't just be a case of writing a new database abstraction - they're different beasts with different applications.
Maybe as a possible place to store log files? After a couple of million rows the mdl_log table gets cumbersome. We actually prune out log table every so often, but would like to keep it to do some statistics.
Maybe having the ability to have the logs be sent to a log server would be better. NoSQL and Bigtable would seem ideal for that case.