I was about to add sitemaps in v3.7.1 but I'm having a hard time trying to figure out why is that hardly needed regarding SEO or more specific Google indexing.
In the demo website I've the following stats:
So we are talking about 25,669 content URLs (images + albums + users). You have to add those extra URLs like /<user>/liked, etc so the number should be near 35,000.
In Google I've 37,266 indexed pages and as this graph shows, the indexing rate is solid as the website grows:
You can corroborate this by doing these queries in Google, it won't get the accurate number but still works to check the number.
Code:
site:demo.chevereto.com > 38,300 (sums everything)
site:demo.chevereto.com/image/ > 18,600 (just public images, private images in demo counts 2121)
site:demo.chevereto.com/album/ > 1,280 (just public albums, private albums counts 342)
At this time Google is missing 889 images for me. That's just 4,6% of the demo public images and is 2.7% of my total crawlable content (35,000).
The Chevereto demo doesn't have a sitemap and still have most of its pages crawled. For those who don't get this index rate in Google I'm afraid that sitemaps won't do the trick for you, sitemaps in Google work in a way that if you have a very large website the indexing will be easier for you in the way that Google won't collapse your website (they do it anyway). At the end Google will crawl you only if they label your website as something that Google cares to index and that depends on your content, website speed, not doing black hat, etc.