I've googled around and found this nice graph:
https://bitcoinvisuals.com/chain-block-rewardAt first glance, the numbers hereon seem to be plausible.
Miners are businesses, they have to pay employees, hardware, power, rackspace, taxes,... so i guess they'll think in FIAT terms.
At this moment, it seems like mining is still profitable, since the difficulty doesn't really make "big" jumps, indicating the global hashrate doesn't grow or drop very suddenly.
With the current preev rate of ~$43k /BTC, a miner makes $268.750 from the coinbase reward.
https://bitcoinvisuals.com/chain-block-reward tells me the maximum income/block was around $400k at the end of 2021. Right now its ~$284k (so on average, the fees result in $16k/block).
The last 30 days, the average amount of transactions per block was ~3500 (
https://www.blockchain.com/explorer/charts/n-transactions-per-block)
Let's assume everything stays static from now on and see what kind of fees would be needed when the block reward goes close to 0 to keep our network "afloat" without a big outflux of miners... $284k (the amount needed to keep the miners interested) / 3500 transactions per block = $81/tx.
So, in order to keep the network "healthy" if everything stays status quo, we'd need a fee of ~$81/tx. That's the current equivalent of 0.00190
BTC.
Now, that's when we speak about a status quo...
- It's very possible technological advances make it interesting for some miners to mine way below the $284k/block income. At this point we might lose miners in countries with high power prices, and maybe the "gap" isn't completely filled by miners from low power price countries... We might be fine with that (the current diff is actually really high. It might be ok if it dropped a little bit).
- it's also possible the btc price rises (or drops). So the fiat value of $81/tx might be way less (or more) in BTC in the future
- protocol changes are also always possible. We had the segwit softfork a while ago that allowed us to move the witness data in the last 3Mb of a block. This increased the amount of transactions in a block. It's always possible something similar might happen in the future
Bottom line: if everything but the block reward stays the same, in a couple of halving we'll need to pay ~0.0019 as fee if we want the same level of network security. If the miners either use new tech, or we're willing to have a little less security, the fee will be lower. If the price rises, the fee will be lower (in BTC terms, not in FIAT terms offcourse).
Anyhow, if we're talking about FIAT, i would not be comfortable paying more than ~5% of the value of my transaction as a fee, so yeah, transactions with a value under 0.04
BTC ($1700 at current rate) would kind of defeat the purpose (at least, for me, and only if everything stays status quo).
So, yeah... I guess in the future we should rely on sidechains and altcoins a bit more than we did in the past... Use bitcoin for "larger" transactions (like opening or closing sidechains, or converting to altcoins, or making "big" transactions). But that's just if everything stays status-quo, and it's just my personal opinion