According to Jim Liu in Routes Online, Brussels Airlines is accelerating the phase-out of the Sukhoi SuperJet 100 aircraft wet-leased from CityJet.
The last flight will indeed be operated on 7 January to and from Billund.
Here is a list of the ultimate flights and destinations, as per Routes Online and FlightRadar24:
Brussels – Basel/Mulhouse: last flight 04JAN19 (SN2705/6)
Brussels – Birmingham: last flight 31DEC18 (SN2037/8 EI-FWF)
Brussels – Billund: Overall last flight on 07JAN19, departing Billund (SN2249/50)
Brussels – Bologna: last flight 06JAN19 (SN3125/6)
Brussels – Krakow: last flight 06JAN19 (SN2547/8)
Brussels – Milan Malpensa: last flight 04JAN19 (SN3159/60)
The SSJ100 was introduced by Brussels Airlines in April 2017 to replace the Avro RJ100. Up to seven different aircraft were operated by CityJet on behalf of the Belgian company, four of them in SN livery (EI-FWD, EI-FWE, EI-FWF and EI-FWG), the three others kept the original CityJet livery (EI-FWA, EI-FWB and EI-FWC). Some of these aircraft were factory-fresh when they entered into service for Brussels Airlines.
Brussels Airlines started reducing the number of SuperJet flights in November. Three SSJ100s are currently still flying for Brussels Airlines, Belgian airline’s livery: EI-FWA, EI-FWB and EI-FWF.
The SuperJet 100s will be replaced by Bombardier CRJ-900 and CRJ-1000 operated by the Air Nostrum / CityJet joint venture, and possibly also by Adria Airways.
The SSJ100 flights were often plagued by delays and cancellations due essentially to a lack of spare parts in Europe. Brussels Airlines thus decided earlier in 2018 not to renew the wet-lease agreement with CityJet, which itself will phase out these aeroplanes from its fleet.
Nevertheless, those passengers who have tried the SSJ100 were often satisfied with the roomy seats in a 2-3 configuration with very decent legroom compared to other similar aircraft, even if they sometimes complained about the noise. See a couple of trip reports hereunder: