It would do basic checks, but not transaction validation, so it wouldn't be robust as full node, but very low cost to run. It would keep the blocks it saw for rpc access, but also be
Couldn't it be used by bad actors for spam TX amplification? If it doesn't know if the TX is valid, then it someone could make TXs with no funds in the address & so for no cost.
Yes, i was taking a more detailed look at it today, and you're right, there would be no way for it to validate trxs, so it couldn't relay those without spam and getting banned. It