If you had to put this in simple English terms, what is the likely hood of bitmain to be able to obtian 200,000,000 7nm from TMSC in 2021? that means roughly a 1 million S19 or 100EH worth of hash power, if that is possible then difficulty will double, if that isn't possible - it won't, and of course this assumes that getting the chips is the only bottleneck bitmain faces.
So that would be about 100,000 wafers. A few articles in early 2020 I found indicated that TSMCs 7nm capacity is about 140,000 wafers per month.
TSMC's 7nm production capacity is fully booked. Relief may only come when Apple migrates to 5nm in 2H'2020. TSMC's 7nm capacity will increase to 140,000 wpm in 2H'2020. By order proportion, the ranking of customers using 7nm will be re-shuffled. AMD's orders are set to double, replacing Apple as the largest customer [for 7nm]. Huawei's HiSilicon and Qualcomm are similar by order proportion.
If that capacity is accurate, then Bitmain would have needed to secure 6% of TSMCs total production capacity for the whole year to get their 100,000 wafers worth of chips. So possible I guess, but with the Apple and AMD fighting over the 7nm capacity, don't know what scraps are left.