I'm looking to put a small site together and would like a CMS for the static content, but also want to be able to code outside of the CMS (to many bad experiences building modules for Drupal). I've used CodeIgniter and played with Expression Engine a little - and know that ExpressionEngine 2.0 will be build on CodeIgniter...I just wondered if anyone took this approach with the current EE version? and if anyone has any real info on when EE 2.0 is coming out? (if there's other similar approaches I would be open to them).
EllisLab hasn't made any announcement regarding specific launch dates for EE 2.0, and anyone with access to the beta currently going on would be under NDA so couldn't reveal any specifics about that publicly anyway.
EE 1.x can be installed to any directory/subdomain so you can always create areas on your server that are controlled by EE and other areas controlled by custom programming without too much difficulty. The hard part is getting them to share (ie: user session data).
I built an EE site that had a "customer dashboard" feature from where PDF's could be printed with invoices. I did this all outside the EE installation using just clean php.
You CAN also include normal PHP inside any template file and link to your own Classes or Includes outside the EE install directory.
Pretty straightforward.
ExpressionEngine 2.0 is coming out on December 1, 2009. It will use CodeIgniter for plugins, etc. Wait just a bit. :)