This is how many transactions Monero can handle
The average transaction size in xmrchain.net is around 1.8kb.
The average number of transactions (https://bitinfocharts.com/comparison/monero-transactions.html) per day is around 26,600 tx per day.
Take the AVG TX SIZE x AVG TX/D x 365 = 17.5GB/year or 0.0175TB/year
Currently, it would cost roughly $8.75 to store the full Monero blockchain (.175 x 50$/TB)
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According to https://ourworldindata.org/grapher/historical-cost-of-computer-memory-and-storage?tab=table&time=2019..latest the price of a terabyte goes down by around 30% per year.
In 5 years, assuming a similar rate of transactions, the price to store the full Monero blockchain will be $2.2 ($50 per terabyte x (1 - .3)^5 x (.0175 terabytes x 5 years + .175 terabytes) = $0.07).
Let's say that Monero begins taking on 10x the transactions for the next 5 years:
.0175 x 10 = .175 terabytes per year at 10x tx rate
.175 x 6 = 1.05 terabytes
1.05 x 50 x (1 - .3)^5 = $8.82 to store the whole blockchain in 2030 at 10x tx rate
Even with 10x the transactions, the price to host the blockchain would stay the same.
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But let's do the average number of total daily credit card transactions throughout the world for 5 years to see how much hosting the whole chain will cost then. This could be a lofty goal for scalability in the future.
https://capitaloneshopping.com/research/number-of-credit-card-transactions/#:~:text=In%202023%2C%20nationwide%20credit%20card%20transactions%20totaled,1.34%20million%20per%20minute%2C%2022%2C950%20per%20second says the number is around 150 million tx per day
150,000,000 / ~30000 = 5000
50 x .7^5 x .0175 x 5000 x 5 = 3676$ to host the blockchain in 2030 with a 5000x tx rate.
TLDR: We can sustain around 10x the current number of transactions, but beyond that, we'll need to improve pruning, reduce transaction size, decrease digital storage prices, or find some other way around the problem.
If there are any problems with my math please let me know.