Could bitcoin/blockchain be used to create a secure non-3rd party escrow?
I would think it has been asked several times, but not in this detail. The way to use escrow would be a „2 of 3 multisig“ transaction. A search in the forum reveals a lot of links. Also very useful is the wiki and of course the bitcoin.org webpage. There are even wallets providing multisig functions. But still it is not „an easy usecase“. Data has to be exchanged between the parties, and as far as I know, there is no protocol specified. So it is still possible to make errors and loose funds :-(

Oh, and then there is Andreas‘ book „Mastering Bitcoin“, which explains even more escrow (3 of 5 combination). Worthwhile to read, and also online available.