I think some people have misunderstood this change. It's been active for me for about a week, I suspect most others without accounts just haven't noticed.
Clicking on a linked tweet still works, it's only when you then click on another from within the site that it asks you for a login. It's the same approach Quora takes iirc.
I don't have an account, and the change has been noticeable and annoying. It's more than just clicking on another tweet, though from what I can tell they've been A/B testing this behavior (sometimes I get it and sometimes I do not). On mobile, you can't click through to someone's profile from the tweet without creating an account. If the tweet chain is more than 4 or 5 tweets, you cannot read the rest without creating an account. It's prevented me from normal browsing habits multiple times, like reading the ASML twitter thread that was posted on HN a couple of days ago.
I cannot view threads or expand images or see people's responses to threads any longer. This does not compel me to sign up at all. Quite the opposite effect. Twitter is not the ideal place for long form threads anyways. *yes lets just keep adding more 140 character mini blogs to make a long form news posting*
Clicking on a linked tweet still works, it's only when you then click on another from within the site that it asks you for a login. It's the same approach Quora takes iirc.