So modules can always do whatever they want (fill a block, then process when full while filling the net block) and a fair number of them, especially spectral processing ones, already do this. Obviously that adds additional latency to those modules. If that’s what you’re after, here’s a good starting point.
I think what you’re asking, though, is whether the engine itself supports block processing. I’m pretty confident that it does not and will not as of V2; even though it’s feeding the audio device in blocks, those are built sample-by-sample as the engine steps through the modules, then cables.
There’s some (veeeeery early) indication that this may change as of Rack V3, which has (again tentatively) been described as the performance update: see the dev blog here. I don’t think this would change any outputs, though, it would just potentially speed up processing on subgraphs without cycles (to somewhat simplify the issue…)
PS. The V2 changelog is here, by the way.