IMO, we will not need massive quantities of such read outs & they will not be required in every possible cell context. There are effective strategies for learning from a few deeply profiled cell contexts (eg. cell lines) & transferring to all other cell contexts. 4/
This means knocking down / ablating regulatory elements, inserting elements in new contexts, arbitrary rearrangements, swaps, deletions etc in several cell contexts with coupled chromatin / RNA / cellular read outs. 3/