When I was waiting to collect my car from its annual service today I asked a sales rep at Holdcroft Honda in Warrington about the Mk4 - especially when it would be released. He said they had a big stock, nationally, of the old Jazz to move on hence all the offers and heavy advertising you are seeing at the moment and this might influence the release date. He expected to see one at a Honda event for sales staff in March and the first demonstrators would arrive in dealerships late April/May time. No idea yet as to specs or prices but he expected an uplift but for the car to remain in the same ball park. Currently a base Jazz with a manual transmission was around £15,500 with the EX topping out at around £20,000. They tend to think the new Jazz will straddle this price range possibly starting at £17500 (ish) and topping out at around £23,000.
I mentioned, by the by, that the Honda EV looked as if it was going to be pricey and he said well north of £30,000. He described the market for this car as "niche" and they didn't expect to sell the car in any volume.