I think that the Lightning Network will still run up against a bottleneck: the bitcoin blockchain. That leads me to think that some other coin will usurp Bitcoin before it can become a defacto currency.
I also would prefer not to have one overwhelmingly dominant currency. I think there is room for at least 2 or 3 dominant currencies, maybe even 4. But to have one dominant currency like Bitcoin will lead to centralization of power.
But even if Bitcoin becomes "the currency" there will always be other currencies to use. I don't think the others will ever go away.
Good thoughts and good point.