I am fine with EIP1559. If ETH becomes deflationary, it would still have other uses and something else can fill in the "currency" use.

Intuitively (have no idea how to do this), it would be interesting to have Country's coin supply grow (approx.) with its GPD/productivity.

What happens when eth switches to PoS? everyone will be incentivized to hoard and stake to become a validator, what will incentivize spending?

APY on stacking won't be as good as today. I am not sure everyone will stake once ETH2 rewards will be around 1-2%.

ETH2 won't be deflationary because such things is nearly impossible in a PoS network. You need issuance to rewards validators. It can't be network fees because if network fees are high, the network is doom to fail.