You say that as though being an eCash system and digital gold are mutually exclusive, or as though Satoshi had no idea Bitcoin would be a good store of value when he created it. That said, I do believe systems can become something other than what they were designed for. I don't see that being the case for Nostr, though. At its core, Nostr is still a permissionless and censorship resistant protocol for communication (free speech) of which zapping is just one expression. The ability to zap anyone you want with small amounts of sats is really just another form of free speech among the many that are enabled by Nostr.