Nucleus should use UTF-8 internally. Please, if you have any experience with internationalization, help with further discussions on this subject.
Timezones: instead of using a 'server offset' like Nucleus 3.x does, timezones should be specified by selecting a region from a list. More thoughts:
Daylight Savings Time (DST) should be handled automatically
GMT+xx is more flexible than servertime+xx
Don't forget about 'half' time zones like GMT+3.5
These are part of the Nucleus 5 plans. Read more about the project.