No government would ever allow coins like Monero to become main forms of currency.

It depends on what you mean by "allow" and "main form of currency". Afaik, in the US (and the rest of the west), at least, there are no laws regarding what form the medium of exchange should take for the exchange of goods and services. The dollar is simply the standard currency to make payments to the government. For example:

United States coins and currency (including Federal reserve notes and circulating notes of Federal reserve banks and national banks) are legal tender for all debts, public charges, taxes, and dues. Foreign gold or silver coins are not legal tender for debts. [31 U.S. Code § 5103 (archive)]

Accepting random alt coins would also come with the expense of having to track them and their wallets separately, exchange costs, volatility, etc, so over time just a few will become generally accepted by businesses.

Is that just a statement of fact, or is that supposed to be an argument against Monero? I'm not sure what the point of that statement is. In any case, I don't see any issue with that outcome — it would simply be a market decision.

And yes, the most likely consequence of long-term crypto usage is that users will centralize into a few trusted platforms who will get the Lion’s share of tokens and power.

I'd say that this is still TBD, but yes centralized control is a concern, as it would break the current designs of cryptocurrencies (as far as I currently understand their designs, that is). Though, note that there is a difference between central ownership of coins in circulation, and central ownership of the network (of course depending on the design of the network — I feel that proof of stake would be vulnerable to this).