read_sparse_block() has been around for years. It's a generic function defined in the DelayedArray package, with several methods defined in downstream packages like HDF5Array or TileDBArray. It is not meant to be called directly. You should always call read_block() instead. See ?S4Arrays::read_block for more information (read_block has moved from DelayedArray to S4Arrays).
That being said, I recently introduced the read_block_as_sparse() generic in the SparseArray package. It will be a replacement for read_sparse_block(). The difference is that read_block_as_sparse() will return a SparseArray object (typically an SVT_SparseArray), whereas read_sparse_block() returns a SparseArraySeed object. This change is part of the plan to use the new and efficient SVT_SparseArray representation everywhere internally in the DelayedArray framework to handle sparse data, instead of the old and inefficient SparseArraySeed representation. This is a work-in-progress. See https://github.com/Bioconductor/DelayedArray/blob/devel/TODO for a detailed roadmap for this transition.
In other words, this is DelayedArray's internal business and the impact on downstream packages and other client code should be minimal.