From some extensive work I did for a customer yesterday, it appears that they are indeed starting to block access from several well known hosting providers (so far, I've seen OVH, DigitalOcean, Hetzner impacted). As part of this, I ended up configuring squid proxy on a VPS server from a lesser known provider, which allowed the images to be fetched by
@AndyB 's Convert Image All addon.
Following on from this, using
@digitalpoint 's Cloudflare app addon and using Cloudflare workers for the image proxy still allows connectivity to Imgur (can't see them blocking access to Cloudflare!).