Wonder where you got the idea for this? 
Absolutely fantastic that core is paying more attention to image delivery and presentation. I like the direction!
(If this doesn’t fully replace Topic List Previews, there is now at least potential to eliminate a lot of bespoke API work from it which I won’t have to maintain anymore, great stuff!)
PS I just tested it and one thing that would be quite nice is if Polls generated a thumbnail so the charts could surface …