I really don't see this as a major risk because the Nigerian naira has been a mess over the years just as you have pointed out, but in other to be able to buy Bitcoin, you need to change the naira to dollar, just that the purchasing power will reduce compared to before, because before we used to buy one day with six hundred naira, but currently speaking it's now #1548, the biggest benefactor of this spike in price is those people that has been holding the us dollar for sometime now before the spike are the biggest winner because their purchasing power are still intact.
So I think that paying attention to how low a country currency is, is just a baseless excuse not to invest in Bitcoin.
You speak like a good investor because if we are to go by what OP is saying then we all need to wait till the currency has returned back to the original state it was before we can start buying Bitcoin with our currency. Such a baseless excuse as you said

Let me make it very simple for you to understand. I am not saying that you should not invest but make your alternative calculation before investing. You can invest at all time. And the risk is always on you not another person. And if you don't know you have to know now. The fluctuation of US dollar affect bitcoin investment most a country like mine and those countries that have the same fate with mine. Right now $1 is N 1,548 and the price of bitcoin is $94,750. And my interest is not even bitcoin but $/local currencies. If you invest now and you invest with $2,000 now and in 20 years to come bitcoin hit $700,000+ in my country $1/N100. Do I gain or do I lose? This my point please understand before commenting. You are free to invest at all time and wait to 100 years to come.
This is just a wishful thinking because you and i know that the reason why we are investing in bitcoin is to save our money from inflation which Fiats currencies are likely to suffer over the years and from your analysis, we know that unforeseen events can happen in the future which can make the local currencies to gain value over the US dollar but i know that you are just giving an instance but let's be realistic here, do you think that your local currency can gain so much strength against the dollar in 20 years time? definitely NOT gonna happen.
Even from the calculations you gave above, you still look lost because if the price of Bitcoin skyrockets from the $94,750 to $700k+ in the next 20 years, regardless of your currency conversion rate against the dollar, it will still be profitable to you because there will no longer be inflation or it has reduced to the minimal which means the cost of living will also be lowered as against how inflation drove the cost of living when the price of your local currency was 1,548 naira as against the US dollars. I don't know if am making a sense to you here?