Increasing the block size is one potential solution but the projections that "the security model" is somehow compromised by no longer having exponential growth in value is a hypothetical thought experiment with no real backing. If you compare to real world mining of minerals of value those minerals don't have exponential growth in value over time. They have a steady growth and value controlled by supply and demand and augmented by inflation. Yet huge amounts of capital are spent constantly in order to mine these to sell them in this market that does not have massive growth like Bitcoin growth.

Even as growth tapers off because there is already value held there is incentive to maintain the integrity of the blockchain. What is the incentive to maintain the price of gold? The current price of gold has risen a lot but not at Bitcoin levels but it is far above the industrial use of what gold would demand. Those that own gold at a large scale, Banks and governments, have an interest in maintaining its value above its industrial use value so it can act as a physical store of wealth. Now we all know that alchemy isn't true but if we hypothetically say if you could control 51% of the gold market you could then be 51% of the gold market you could then be substitute an imitation product for the real thing and because of the control you have you could insist that it is still real. This is a disincentive to everyone who values any kind of market stability and capitalization. Because if you get caught doing this, which you will, not only have you destroyed the value of your imitation but you've destroyed the value of the real thing because trust is lost in it.

The only people who have an incentive to fundamentally break something like gold or Bitcoin or comic book super villains. The US government certainly has the budget and the power to be able to do a 51% attack and wipe out all faith in Bitcoin but they have no incentive to do it. Most other businesses or governments around the world that have the budget to be able to do that also have no incentive to do it.

So while there may come a time when increasing the block size is something that's required to make the network better I believe that is many years off. The doom saying about Bitcoin has been around for a long time, but people often put their faith into a thing and can create it as a store of value far beyond its worth. Why are diamonds worth so much? Why is gold worth so much? Why are many of the precious metals worth above their actual use case values?