Using CBECI numbers, 7GW is about the theoretical lower bound (i.e., everyone using the most efficient hardware available). The upper bound (i.e., everyone using S9s) is about 34GW. Current best estimate by them is 16.6GW at this moment. It's really hard to know as shipments of new, modern ASICs are increasing (see total hashrate), and nobody knows (yet) how much of the old equipment is going to be finding new homes, which can take months between when powered down at one site, refurbished and tested, then bought and sold on secondary markets, and eventually powered back up at its new home (possibly in another country / continent).