Only Dragon Quest 11 DLC and some updates require FW 9.0 right now, I'm sure there will be compulsory 9.0 games in the near future. FW 9.0 added stylus support and Nintendo started selling stylus recently. But until then, I'll stay at 8.1.
hmm I'm sure stylus has been working previously.. my daughter would use the stylus on the switch becasue she was so used to using it on 3DS