Unlike all GUI apps out there, this one gives you the ability to write one, using the interface as an API. Go for it!

There are various projects that use a similar file format and approach, this one has a web ui:

http://hledger.org/

I'd like to be able to access a ledger over the web, but really maintaining the ledger in a text editor, putting it in version control, etc., are, I find, a pretty efficient workflow, better than a more typical web UI for this particular use.

A "web UI" that consisted largely of a browser-hosted text editor with, perhaps, some ledger-specific affordances, some facilities for pre-defined reports plus a way to create new reports with customer ledger commands, and a decent history interface (possibly backed by a traditional VCS) would be nice, though.