There are no plans that I know of, but I would be surprised if Katakana (and even Hiragana) does not change over time. Writing systems tend to change with time, to better reflect natural changes in the languages they represent. So the real question should probably be whether there will be a change soon.
And maybe there will be change soon, since already some Japanese can perfectly distinguish between [si] and [shi], snd it seems like the Japanese government isn't too conservative about small changes to the gairaigo spelling rules.