Bigger block, regardless of how it happens or what size, will need to happen via a fork.
And let me be very frank here. Coming from someone who has organized not just one, but multiple forks logistically with Litecoin and Dogecoin I can tell you its not all doom and gloom as people have claimed it to be. It's a pain in the ass, but not the end of the world. I'm one of a few people within cryptos who have experience in doing this.
Hell I'll state right now that I will personally help with the fork when it happens for Bitcoin.
Nice to have someone with experience.
Can you tell us a bit about the issues you faced? Particularly what can go badly wrong.
The largest issue I have personally have run into is communication. Specifically,either conformation from entities that they agree to the confirm to the new protocol or language issues. Language issues can be resolved with the addition of translators if available (which in Bitcoins case I cant imagine is that hard). In terms of the agreement is a little more difficult, and usually involves more "harassment" of said entity. Finding email addresses of entities is also a large pain point as well.
In any case, I would imagine it would be easier to upgrade bitcoin to a fork, but only if certain entities are supportive of it. For example, if BIP100 were to be the one that gets forked, it would be easier to send emails and CC TBF so those who receive the message know its serious. In cryptos, those who hold leadership positions in the ecosystem are the ones who influence the fork (yes I know its counter to decentralization, but thats another discussion) .