I don't have a Twitter account, and this now makes it far, far less likely that I will even click on a Twitter link or engage with the platform whatsoever.

I could obviously be in the minority (though I'm certainly not alone), but I'm curious if you think that my scenario will be the less common one and this will actually increase signups, or if it will have a positive impact on the stock price in another way.

Yes I do think this will boost sign ups. It's free and Tweets, for better or for worse, have come to be a sort of "source material." I think many, particularly younger, news-savvy users will seek to access Twitter.

I also think it greatly boosts Twitter's ability to monetize advertising. That's what make Facebook and Google so valuable (just about everyone is logged into an account).

I am, however, curious how this will impact embedded tweets (in articles, for example).

Why do you think this is good for the stock price?

Everyone is logged into an account + Tweets (and share buttons) embedded all around the web -> way more data for advertising.

That's the underlying fact that make Facebook and Google (and to a lesser degree, Pinterest) so valuable for advertising. Facebook and Google have organic signups (FB for FB, Google for Gmail, Youtube, etc.), but Pinterest does what Twitter's thinking of doing here--it locks you out of content until you have an account. Pinterest also has "share" buttons (and the accompanying JS, cookies, etc.)

You're a shareholder seeking short-term gains. That doesn't really absolve you of this opinion.