There are a couple of mods here and there for fallen london, and also for this forum. Most of what i’ve seen is custom Style Sheets, to do things like making it impossible to discard certain cards. there is potential for modding a web application for FL.
As can be seen here:http://community.failbettergames.com/topic21710-user-style-opportunity-protector-pending.aspx
And Here: http://community.failbettergames.com/topic20311-user-style-lily-protector-pending-approval.aspx
People are making little threads for their mods, for feedback, improvements suggestions, etc.
It probably wouldn’t be especially high traffic, but it might be nice to have a modding subforum. It would also be a nice opportunity to give it another cool name
Perhaps Caminus Yards, or Cotterall and Hathersage. Or the Great Downward Engineering Company