I like it. We need more experimentation with bitcoin nodes. The biggest problem is recreating bitcoin consensus logic. You basically can't guarantee it will stay in consensus, so that's a bit of an issue...

You could probably get very far with blocks only mode. It has a mempool so you can simply drop every transaction you aren't interested in and keep the ones you are watching for via sendrawtransaction.

Not sure how you would learn about the transaction if your node isn't listening when it floods across the network. Perhaps a mempool nostr relay that just replays transactions as nostr events.