I think OI certainly is a fork of Icon - actually the code started as
my out-of-date and locally modified copy of Unicon's cvs tree,
although there is very little Unicon code left now in the OI code.
I think it is also accurate to say OI is "OO-Icon + Unicode" (although
I chopped out a few things along the way too, so we should add " -
some other bits" to the equation).
As to Icon 9.5, I doubt very much whether there will ever be another
major Icon release. I don't think the Icon source code is being
developed any longer, at least not in any major way. I do notice
however that they still occasionally add things to their website (the
technical reports list in particular has grown longer recently, with
some very interesting additions).
Kind regards
R