From the horses mouth: An email sent to suppliers on 11 January clearly states that it is the 600 series of ink, not the 610 series of ink that will be discontinued at the end of January 2019, with last call being December 15, 2018. Most people with that machine upgraded to the 610 inks which will still be around (although, according to the same email, will see a 5-10% increase in price, starting 11 February 2018).
The discontinuation of the generation 1 latex ink (the 600 series for the LX800/850) is also bad news for owners of the L25500 machines as they use the same ink.