Given that the fediverse is very likely to have an enormous influx of users straining the infrastructure, automatically expanding images beyond the thumbnail would compound all the instances, so I don't think that I would recommend making that available yet, or at least until some more maturity has been developed into the platform and architecture. I love the idea, and I also find it annoying to have to manually open each of them, but maybe a bit of a slowdown on the doomscrolling is a good thing.