Considering XCP is burned for fees and no new supply … will there one day be no more XCP?
Practically speaking: No, never!
One XCP consists of 100,000,000 indivisible satoshi-XCP’s. It’s the same as one BTC contains 100 million satoshis. There will only be a problem if the indivisible satoshi-XCP gains a significant value. For example, it would be a problem if a fee is 1 cent but a satoshi-XCP is worth 2 cents.
For this to happen one XCP would have to be worth a whopping 2 million dollars !!! This, of course, will never happen so the problem in only theoretical.
A real concern, though, is if fees are hardcoded fixed XCP amounts. Problems will arise if the XCP price increases a lot. This can well happen - for many reasons. Hoarding, speculation, demand for DEX currency, demand for lotteries are some reasons. The scarcity effect from burned XCP fees is imo negligible.
The solution to these problems is to have the protocol adjust fees. This is pretty simple if we can agree on hardcoded technical target values. With Bitcoin the mining difficulty does just that. It adjusts automatically to reach a hardcoded 10 minute block time.
I think during the EVM discussions we’ll probably eventually reach this discussion to, so that’s why I haven’t brought it up yet