As pointed out by @ashley in a conversation, [[https://www.mediawiki.org/wiki/Extension:TextExtracts|TextExtracts]] is what Snippet does, except with more functions and more flexible. Deprecating this extension should be a slow process since outside sites use the Snippet API, such as Brickset (I think there's more, but I can't think of any). CC'ing @georgebarnick: Do you know what other sites use Snippet?
Besides LEGO sites, it looks like it's being used also on a site called "Wikidébats", [[https://wikiapiary.com/wiki/Extension:Snippet|according to Wikiapiary]]. It's pretty active too, looking at http://wikidebats.org/wiki/Sp%C3%A9cial:Modifications_r%C3%A9centes
Doing this to this extension will also require changing:
* Changing some wiki pages:
** https://www.mediawiki.org/wiki/Extension:Snippet
** https://wikiapiary.com/wiki/Extension:Snippet
* Possibly archiving:
** This phabricator project
** The gerrit repo for this extension