I don't think it'll affect things too much really. I saw a fun suggestion on Twitter, where someone said that forearm riding should be allowed once a solo rider had a gap of x seconds on the peloton or something, which would be an interesting take on it. It's not a mega Zwift aero boost style improvement the way most people do it (arms too low, elbows too wide) so not really going to change anything.
With the downhill position - we have seen it help especially in stages races for the odd extra second or bridging to a group ... I'm ambivalent really about whether it should or shouldn't be banned. We have tested it a fair bit in the wind tunnel and it is a lot faster than being in the drops etc.