It's not easy to upgrade from IPv4 to IPv6. It's not easy AT ALL to move from TCP/IP to another protocol.
Very easy to move from bitcoin to futurexxxcoin. It's a simple program on a machine that you can delete. Install another.
It's still very easy to move from bitcoin to any alt-coin, try it and see the difference
going from bitcoin to a scamcoin you will open up yourself to potentially lose money from an attack on the network and will almost certainly lose money from value depreciation of your scamcoin.
When you go from IPv4 to IPv6 you are gaining more features and will have more security
The problem here is not how hard it is to switch.
But if it will be worth to switch. That is what network effect is about.
Yes, you can switch over to laserdisc.
But how many people did switch from vhs to laserdisc?
Very few, why? Because they couldn't really find many titles to watch, why? Because not many people was adopting it.
The network effect of bitcoins will have the same effect.
You might be able to exchange it to litecoins or dogecoin, but if there aren't stores that accept it and there are no people who wants it, nobody will be exchanging it to that currency.
On the other hand, if another currency becomes popular (let's say dogecoin), regardless of how inferior it is technically, if it becomes extremely popular commercially, it will become dominant.
The only thing that matters is the network effect, its adoption rate.
The moment to compete against bitcoins is right now.
If there isn't a challenging altcoin in the following years, it will be really hard, even impossible, to take bitcoin down.
There are two aspects that fuels the network effect: a new conformity and a cognitive inertia.