4 years is a long time.
The first four years were a lot of time, when we brought into circulation 10.5M coins. The second four years were also a lot of time as we brought into circulation 5.25M coins. As time passes, the four years after a halving becomes less effective if you assume that time is what affects the supply. For instance, between 2036 and 2040, the supply will change by 82,031.25 BTC which is sixteen (!) times lower than this epoch's change.
So answering to this:
There is a reason why the decrease in block rewards is the most significant at the start and starts to taper off as we reach more milestones.
It is clearly a cause of the supply and the demand. Once the supply affects lesser over time and the demand will have reached a global scale, there won't be any milestones. There'll be stabilization. Thus, the drop off of those sub-groups won't be temporary.
As far as I've understood, they re-enter the game due to the price increase. Their earnings are far more than their costs.
In 8 years, if we're facing a problem where we still don't have enough on-chain transactions or still cannot meet the needs, then I suggest that we should just ditch Bitcoin as an experiment.
There will probably be lots of on-chain transaction with or without the development of off-chain solutions that satisfy mainly micro-payments. What are the needs you're talking about?
I don't agree that the incentives will decrease to the point that it becomes a threat to Bitcoin's security. The block rewards will decrease over-time, that isn't really disputable. Just look at the numbers. I don't agree that the drop in block rewards cannot be cushioned through other means.
I agree that it may not become a threat to Bitcoin's security. I disagree that I should make my assumptions by looking the numbers during the first years of its appearance.
There is no reason for concern until we reach a point where it becomes easy or feasible for an attacker to attack Bitcoin. Do you agree?
Do you agree that we should discuss about this possible scenario as a community and acknowledge our options? Even if it might never be feasible for an attacker to destroy Bitcoin that way, shouldn't we cover the arguments that go against it?
At least, if we're supporters of it.