I was initially really against this, but parent comment brings a compelling argument: people are already using the service to say more than 140chars worth of stuff. The current methods to do it result in a far worse user experience than the tried and true "Read More" button would.
That said, I'm skeptical of it just in terms of product definition. Like Instagram adding portrait/landscape photos, more than 140 characters to a tweet does nothing but obscure what exactly the product is and how you're supposed to use it (even if people circumvent that anyhow).
UX is something many businesses seem to really struggle with. If unnecessary friction is added, it really should cause stakeholders and designers to pause. The "read more" CTA will lead to more truncated tweets within the first 140 chars, something that is visually unappealing and breaks the reading experience by forcing a manual action. The workarounds you describe are not used by everyone and I'd wager that most users simply keep their posts within the 140 char limit rather than pict-tweet or storm a longer convo. Yes it forces brevity, but that is the Twitter identity which supports the product's skimmability usefulness. Give users a read more option, and many will post a few extra chars just because they don't have to put much thought into their wording now. Short term: usage goes up. Long term: quality decreases as Twitter becomes just another Facebook or Medium. It will be worse than Medium though because the audience Twitter is going after is more generic.
I've always argued that Twitter's userbase is more influential and valuable because of its forced brevity and fact that it was unique.
I already avoid truncated tweets and want to read long-form content elsewhere. So, I won't be using Twitter more. Maybe others will, but again, I'd wager that Twitter is simply sliding down a path that will be ultimately more harmful for its long term sustainability.