In some cases yes, but I don't think you can get away with client side validation for a lot of things because they depend on the state of your database to return the correct result.
For example, how would you validate an email or username on the client when the availability of the name depends on you making a database call to see if a user exists already? You have to make a network call, get the result and then update your validation errors on the client based on that server side result.
But for validating something like a phone number or twitter handle, sure, client side works all the way but I don't think having even 200ms of delay for that validation is going to make for a bad user experience. 200ms is a lot too. That's about what it takes to ping a server in Tokyo from New York.
Your other points are valid tho. I guess we'll see where LiveView ends up going.