Add syntax coloring for UserTalk, Python, etc. (Perl, PHP, Java...)
Add syntax coloring for HTML/XML.
Basic auto-completion.
Development / IDE
Support Python as a first-class language.
Provide a simple way to call Python libraries.
Provide a simple way to call Java libraries.
Integrate basic version control, including diff.
Object Database
Save to disk without locking other activity.
Improve performance and stability, e.g. see UserLand's note and the followup discussion.
Platform
Compile on Linux: a "runtime" version with minimal GUI should suffice.
Components
Create a standalone outliner.
Create a standalone UserTalk interpreter (perhaps running on the JVM).
Internal Changes
Remove folder path from the address of a root file (and/or provide other ways to make multi-root projects portable across folders, hard disks and machines). Note: I'm still using an old version; perhaps this problem has been solved?
Business Issues
Applications
With Python as a first-class language, Frontier would make an incredible tool for teaching Computer Science. Realistically, most schools would prefer Java -- which could also be done.
Funding
Find a commercial sponsor, e.g. a large company that uses Frontier internally and would benefit from ongoing enhancements.