Great news, as far as I'm concerned. Without wading into the politics of Brexit and the implications on car building that might bring, the brass-tacks of this means that Ineos now owns a car plant rather than having to build one from scratch. That moves them MUCH closer to production than they were a month or two ago, and makes it a lot more likely that this will be a real vehicle we can buy next year/early 2022. Plus, there's something to be said about a workforce that is used to building Mercedes -- that's not exactly a bad thing in terms of quality. Granted, the car in question (Smart EQ Fourtwo) isn't exactly heralded as the pinnacle of motoring, but the critiques I've seen on the Fourtwo are mostly based on design, not quality control/production.
I know that, being the 'spiritual' successor of the Classic Defender, having it not built in Britain will be a mark against it for some folks, but I still see this as very good news.