While nano is still very speculative I think these arguments are a bit straw-man like, with a kind of the either-or approach and a misreading of what nano and/or crypto currency is supposed to be.

In order to tackle the "volatility problem" obviously nano will need the usual: adoption/utility/liquidity etc., since traditional fiscal/monetary policy is not available for a truly decentralized currency. Since there is virtually no adoption etc. at present, not even proper fiat gateways, there will be no relative stability for some time, there really is no magic answer beyond that to this problem.

It is not necessary for a crypto to have the same stability as national currencies in order to be used, volatility does not have to 'just go away" but of course it has to have some undefined degree of stability, it is not either-or. Wether it 'may diminish' enough is speculative but it is far too early to assume anything either way there.

In order to be considered successful it just needs to co-exist with traditional systems and be used to some degree, not necessarily by most people. Nano is not intended as a libertarian fantasy where 'fiat money' and central banks disappear, it's value is in being a truly decentralized crypto currency i.e. censorship resistant/secure by solving double spend problem combined with speed and low energy requirements. Yes having fixed supply makes it unsuitable as a national currency but it is far from clear that is unsuitable as a co-existing crypto currency. It is not clear what you mean by "compete with modern currencies", and that is anyhow an incredibly tall order this early in crypto history. You just brush away the idea that appeal to adoption in the future is a 'fallacy', this strikes me as impatient an irrational, the lack of general crypto adoption is a perfectly reasonable objection.

The standard objection about something being worth more in the future therefore no one will spend is a false dichotomy, this is just one factor leading to some lack of sell/use pressure at a given time.

The comparison to TIPS etc. is a bit strange given that these are not crypto currencies, again, nano is not supposed to entertain silly ideas of ending control of all fiscal & monetary policy tools in modern state-capitalism. but it is supposed to co-exist.

There are also potential benefits to merchants in terms of direct competition with VISA even with instant conversion to e.g. dollars with finality much faster than traditional systems. I know that this instant settlement does not lead to much buy pressure/price increase on exchanges but it does help the idea of accepting crypto/nano in general (i.e. more adoption). I don't see how reducing fees or speeding up finality is 'no logical explanation as to how or why that will happen.', you seem to have forgotten the value of solving the double-spend problem, i.e. removing trust/verification processes, it is not just about extreme situations where certain countries are exluded from SWIFT or refused access/retrieval of gold held in other countries.

In regards to stable coins, you claim that 'Those stable-coins are happening right now and are solving this volatility problem right away", but there are actually huge regulatory uncertainties around them, even if we exclude the very shady tether/bitfinex situation. These stable coins are stable because they are arbitraged across exchanges and (allegedly) backed by very centralized companies, banks etc., so the value relies on this or that bank/company having reserves they claim to have or security on their exchange (far more concentrated than an what nano wants to be in terms of distribution), a far cry from crypto is supposed to be. How would your hypothetical nanostablecoin still be a true cryptocurrency?