I guess if you already have a 9900k this is mild upgrade, will still cost at least £200 to do so though assuming prices in the market and the assumed price this will release at ($600?).
Anyone who 'upgrades' to the 9900KS from a 9900K falls into the category of being certifiably nuts. If they really feel the 9900K isn't fast enough then they'd be far better off just saving the money and putting it towards the new 10 core chips coming in Q1 2020, with the new Z490 sockets.