If I would be a miner I'd provide a service Submit here your defense transaction and we split the punishment fee, which is then a win for Bob and for the miner (but stolen funds from Alice).

In that case the defense transaction may as well go to https://opensats.org/ as that would be imo more trustworthy trusted party than miners :)

Or rather in the case of conflict you would go to some trusted arbiter (agreed on ahead of time) that would get the coins, get some fee and divide the coins back to you based your transaction logs...