An idea I had about network congestion was that transactions could pre-buy block space.

A block size rule of this type would be 10MB per block total size, but all blocks are capped at 1MB "modified" block size too.

Normally, a transaction's modified size would just be the size of the transaction.  For each output, it can add additional loading.  This increases the modified size of that transaction but then decreases the modified size of the spending transaction.

A 500 byte transaction could have an output that is loaded at 500 bytes.  That transaction would count as a 1000 byte transaction for modified block size purposes.

If the output is spent by a 490 byte transaction, then that transaction would count as -10 bytes.

Essentially, the transaction's modified size would be

actual size + sum(output loading) - sum(input loading)

When loading an output, that transaction costs more but then the spending transaction costs less.

This means that the channel open transactions could be loaded so that the channel close transactions don't actually use up block space.

If there was a lot of congestion miners could still include up to 10MB of channel close transactions per block.  The average block size would be 1MB but could be increased by 10X in an emergency.

tl; dr: I propose replacing the hard cap on the data size of a block (1MB, 20MB, or whatever it is) with an elastic one, where resistance to larger blocks accumulates progressively. Miners will be required to pay a superlinear penalty for large blocks, to be paid into a rollover fee pool. This will greatly increase Bitcoin's robustness to a situation where the block cap is approached, and allow a healthy fee market.