In a lot of regards, renaming a topic and the URL changing isn’t a major issue because it redirects properly. Topic routing is based on topic id, so even if you type in https://meta.discourse.org/t/donk/162580, you still get to this topic. That topic id will not change from any user interaction on the site.
If the URL 404’ed, sure, SEO and social would be a problem, but it doesn’t – it redirects and Google will properly update the URL.
We do recommend all community managers update titles to accurately reflect the contents of the discussion. This is good for both SEO (as the biggest factor in ranking is matching search intent with page contents) and discovery/participation within the community itself.
For more on how we think about SEO: