Using your shared UTXO example, let’s say we’re using CTV, and you are  guaranteed 1/10 of the coin. Somebody has to publish that transaction to get the coins out. For a miner to mine it, the fee must be paid by one or more child transactions whose fees cover both themselves and the parent withdrawal TX.

Now, if you’re in a hurry, then you’re the one who has to pay. But you could also coordinate with others to share the cost. This is indeed a problem. It’s an ongoing discussion to figure out how to make unilateral exit cheaper.

The point I was making about block space is not about increasing size. Keeping a small block size is important for decentralization. It keeps the cost of running a node down so more people will do it.

The point about block space being unbounded is that while the block subsidy will run out around the year 2140, there’s no limit to the number of blocks after that. In the fullness of time (centuries), block space continues to grow at 1MB+ per 10 minutes in perpetuity.

Bitcoin rewards patience with lower fees. If you wait, you can move coin more cheaply.