The whole mempool would be cleared in 8 hours of 4vMB blocks, 8 hours!
Even if they will fill it, does it matter if they fill it with 5 sat/b? No. it doesn't, just as it didn't matter when everyone was spamming the mempool with 1 sat/b ordinals, user looked at the size of the mempool, and they saw that 5-7 sat/b tx still got confirmed and nobody really cared.

The whole thing about increasing blocksize and assuming spam will keep with it reminds me of a discussion between the city councils against enlarging a road, their argument was that if we double the lines then we are going to have twice as many cars. I wondered if we increased the lanes ten times, would that mean we're going to have 3 million cars in traffic each day driven by, well, the 1 million people in my city?
It's the same here, why everyone assumes there will be 7 times more people spamming the chain with brc-20 with the same fees?. I said 7 times because right now half of the blocks are still occupied by normal tx, mostly from exchanges batching and consolidating transactions, so spam is just half of this.