Any block size upping will require a hard fork and at this stage I don't see how that can happen in a smooth and unified manner. I think it's too late now.
I take the "dynamic goldilocks" view on this. 4MB blocks (the entirety of which is not currently easy to use, 2-3MB is more realistic given today's way of using Bitcoin) is enough to compete against the competition when you factor everything in, given today's level of adoption. It's not necessarily wrong to say that's not enough, but blocks are nowhere near full today, so clearly the 4MB increase has bought some time. And as Bitcoin may continue in a positive feedback loop of increasing relevance, I don't think it will be as hard to find the level of unanimity needed to make infrequent step changes to maximum blocksize/weight, even though it will likely always be debated and argued over pretty pugnaciously. So it can only change when it's absolutely necessary. This is a good thing. And that may include the possibility that 4MB will always be enough, it depends on what can be done with that much transaction space (current techniques for efficient usage of 4MB suggest it is enough in the medium term, but not in the long term. That is subject to new innovations, of course)
The prevailing view is that it's best for the network to under-provide, given the background conditions (i.e. the health of the internet itself). Because if the conditions become worse (i.e. something happens to the internet that makes it harder to use), then at least we weren't maxing out usage of the internet as of the previous good conditions. This means Bitcoin could survive if the internet goes backwards in usability, and it's impossible to rule that out for all sorts of reasons. Payment channels (i.e. Lightning) would handle this particularly well, the blockchain itself could completely grind to a halt, and the comparatively less demanding requirements of a channel network could function more easily than the base layer. In a scenario like that, I can imagine people cursing even the present-day 4MB block limit as the internet gradually returned to it's previous state of health.
I'd prefer to see a living Bitcoin with a lid on it that forces people to find solutions than one blown apart.
The devs are broadly taking all this into account with their approach:
- Reducing the resources (RAM, CPU, bandwidth) needed to run a Bitcoin node
- Making network level attacks (e.g. the various ways to split Bitcoin into two or more partitioned networks) harder to perform
- Increasing the utility of the space in blockchain blocks (there are all sorts of angles to take)
- Adding fallback modes/infrastructure to mitigate attacks or outages (e.g. redundant network code written differently, or 2nd layer payment rails etc)
There are multiple initiatives going on right now to address all the above. None of it will be enough, it's an eternal cat and mouse game. Every new paradigm begets a new method of attack, despite any ground gained. But Bitcoin has gained and held ground, and continues to do so.
Take a look at Bittorrent; endlessly attacked in all sorts of ways, and yet the developers keep innovating, and the bittorrent network is bigger, tougher and more usable than ever.