I agree. While Series 7 look a bit dated, replacing it with that flat edge design is a regression.The flat design is awful and has always been awful. Please, no.
As for additional health sensors - sure, if they work right. The blood ox on my series 6 is so all over the place as to be useless.
I would prefer all that energy spent on making nicer watch faces instead. Contour is the first truly different watch face I've seen in awhile. Hermes and Nike exclusive faces notwithstanding, most of the watch faces are variations of 3-4 watch faces.