Im wondering if there is an easy way to get a list of all R packages that are currently using RangedSummarizedExperiment object inputs?

Thanks!

Do you need RangedSummarizedExperiment specifically? If not, then you could always look at the reverse-dependencies (and reverse-imports, and reverse-suggests) at https://bioconductor.org/packages/SummarizedExperiment. Presumably all of the listed packages use SummarizedExperiment or its subclasses. Any method/function written for a SummarizedExperiment would also work on an RSE object, so those packages would fit your criterion even if they're not written explicitly for RSE inputs. The only packages that don't fit would be those that derive a new, non-RSE class from SummarizedExperiment; I don't think there's an easy way of pruning them out other than to manually inspect them.