2^64 = 98 years

2^65 = 195 years

2^70 = 6,239 years

No, he meant bits not bytes, he always call bits bytes

COBRAS,

Worst case scenario:
take 2^64 (18,446,744,073,709,551,616) divide that by how many Keys your equipment can check in an hour or day or whatever time; I'll use by day as an example (24 hours). You said you have 6 000 Mkeys/sec, so 6,000,000,000 keys per second equals 518,400,000,000,000 keys checked in a day. Now, divide 2^64 (18,446,744,073,709,551,616) by 518,400,000,000,000 keys per day = 35,583 days which = a little over 97 years.

drop it down to 62, for good measure... 2 ^ 62 = 4,611,686,018,427,387,904; divide by your power per day (24 hours) 518,400,000,000,000 keys = 8,895 days = 24+ years.

at 2^63, will take 48+ years.

I wouldn't say "this would not work"...all depends on how many GPUs you have. And also how you attack it.

Ha! I didn't say it was or wasn't possible with 1 GPU; I merely said I wouldn't say it wouldn't work. He said he had 6,000 Mkey/s which is more than 1 GPU.
To break Bitcoin is easy...it really is. If there was a dedicated pool, Bitcoin would fall. Look at all the hashing power on Nicehash. People renting their rigs. If a pool had 1/10th of that power (non asic algos) bitcoin would fall...meaning the pool could find any/all private coins.

The problem is trust; no one trusts one another and no one would trust the pool operator/creator. But, if someone creates a pool, or site, like Nicehash, that runs bruteforce software, instead of mining software, and people are paid to "rent" their computing power, Bitcoin would fall...no quantum computer needed.

Ok...build the pool and let's see 

There is no power to rent to "hack" as of now, like Nicehash. If there was, I would. But there's not.

I believe it could be done by brute force, but let's talk about the most recent find in the 32BTC challenge/puzzle.

The 2^115 key was just found, in 11-13 days, using 256 V100s. Now, imagine what you could do with 4,700,000 V100s. (rough numbers using hash power of 1 V100, compared to hashing power that is available for 1 algo on Nicehash)

You can say I don't know the cryptography of BTC and that's fine...but all it would take is to "hack" one private key with a substantial amount of BTC and I believe people would start to sell/move their crypto elsewhere.

None. OP meant a private key for bitcoin with a limited search space for the private key of 64, 65, or 70 bits. Or in other words the bruteforce challange from this topic: https://bt.irlbtc.com/view/1306983.0.