I've been thinking about this for awhile now:
System fields are just a pain in the butt.
Custom fields are genius.

1. From a development standpoint every system field has to be treated as its own little animal while custom fields can (except for the pesky cascading select) be treated abstractly.

2. All the System fields have nearly duplicate analogs in the Custom Field world:
Description=Text Area Field
Summary=Text Field
Fix/Affects Version = Multi Version Field
DueDate = Date Custom Field
etc.

3. The system fields always show up on the simple search page regardless of whether they're visible in any projects.

4. Custom fields have great tools for setting up contexts based on project and type while system fields don't.

How about just getting rid of System fields forever?