I think by "2017 rally" they, Forbes, mean a shorter period of time, starting mid September 2017. That's when Bitcoin really jumped big, from $3,600 to $19,000 three months later. And the current rally has started in the end of September 2020, with BTC at around $11k, and if it is indeed a more more sustainable one, we can expect Bitcoin going over $60k in 2-3 months from now.
I don't know whether we will have similar bull run or not, but we can expect it to last at least 3 months. The demand is looking robust right now and if the additional supply is completely removed from the market then $60K or even $100K may be possible within 2021. The current rally is supported by solid fundamentals, so it is very much probable.
All things will depend if the demand would really be there on next year to come.It isnt safe to presume about 60k or 100k in 2021 yet breaking the previous high is already a challenge.
How much more if we do talk into those digits? Lots of reason that people presume out on what happened on that 2017 bull run and then suddenly popped out and crashed the market
going below in 3k and now we do see the similar scenario on rising up the price in last quarter of this year which we can say that it is totally the same in that particular year.
Comparing the news of adoption between those times then theres really some big changes thats why i do see that the price will be tanking somewhat.
I think the main difference between the 2017's and current bull runs is that after seeing the downfall from $20k to $3k, most people became sceptical about Bitcoin future, and it seemed that nothing could make them to believe that BTC will ever recover, let alone surpass the previous ATH. Yet, we are almost there today.
One week after the article form the OP was published, watching how the events unfold, I can say that I agree with Forbes regarding PayPal being the main reason of the current bull run and the sustainability to it.