JS has already adopted the endless style and it’s obvious when to use it and where a single line adds needless complexity. It’s really an overrated barrier to entry with a high return value in code simplicity (particularly aesthetically, which goes a long way with Ruby).
I have no comment on the rightward bit though. That is more... radical. Until I see how it is adopted generally.
I'm not a fan of rightward assignment because I don't see much value and now the => operator has even more meanings.
I'm not a fan of endless methods because how lazy do you have to be to not want to type 'end'? My editor does it for me automatically. Now there is even more parsing.