Fare buckets are dynamic and can change at any point. It's rare if the lowest fare bucket comes back again once zero'd, but it can go from I1 to I9 for example due to sales patterns versus expected sales. If the aircraft is changed it is technically possible for I0 to come back.. Sales tend to not to touch the fare buckets per se, but do give the option of a cheaper ticket within an existing bucket. So an I fare will become available at say £200 less than before.

Note the current European sales dates if you are prepared to start from elsewhere in Europe:
Wave 1: 17 Aug - 14 Sep: DK, DE, FI, SE, NO, BE
Wave 2: 24 Aug – 21 Sep: FR, IT, RU, NL, CH, AT, PT, HR, GR, CY, BG, RO, PL, CZ, HU, IL, TR
Wave 3: 1 – 18 Sep: ES