More of a shower-thought, but I am currently working on a bitcoin wallet that is designed to handle "free pressure" properly (e.g. CPFP aware, transaction merging, automated progressive fee bumping, etc) and one kind of annoying thing is that there really is no fee market on testnet.

I was thinking it would be cool if tesnet blocks were a bit smaller, so they didn't just mine the entire mempool each block. A full-blown softfork on testnet seems overkill, but just changing the default mining maxBlockWeight to something like 50% of the current mempool weight would help test things and help wallet developers fixing things like "stuck transactions" and what not.  (And of course some miners will not use the default, but it's not really a big deal..)