Thanks for the reply. I agree with your assessment of the issue, and I had thought about it too. The reason I still believe it's an issue though is because I observed that a large part of the time, the incomplete sentence actually caused me to open the link in a new tab to see what the next word was, thus defeating the very purpose of the preview. If many other users have also experienced this same behaviour, it might be worth fixing it.
To explain better, considering the example provided in my original comment, the preview ends with "holds a collection of priceless", which immediately begs the question: priceless what? Whereas, using the rule of only including complete sentences but not crossing the word limit, the preview would reduce to:
The Uffizi Gallery is a prominent art museum located adjacent to the Piazza della Signoria in the Historic Centre of Florence in the region of Tuscany, Italy.
IMHO, this brief extract fully serves the function of a link preview, without the added "discomfort" of having a broken sentence. An ideal compromise might be to add a setting to "Include full sentences only" in the page preview preferences, but I'm guessing this might unnecessarily complicate matters.
Essentially, I suppose it boils down to seeing which option more users prefer: a shorter but complete paragraph, or a longer but broken one?