I want to know what you guys think will be the biggest event for bitcoin in the next 5 years. What problems will be solved, what problems will arise,
I think we are going to see more adoption and more regulations over the following years. Consequently there will be a lot of growth in both popularity and efficiency of decentralized exchanges as the demand for them rises specially to trade altcoins against bitcoin.
I also hope for more adoption of second layer so that we can see less spam on-chain from big centralized services such as exchanges and gambling sites that would help scaling a lot.
will mining centralize more (maybe in the US?) or disperse across the globe?
If you look at the way mining has been spreading across the globe and becoming more and more decentralized every year you realize that the trend will continue. I also don't see any reason why it should reverse.
When we talk about "bitcoin transactions", will we be referring to on-chain, or lightning transactions (i.e will lightning be more relevant to the avg user than on-chain)?
On-chain transactions will always be more relevant than second layer, and that will never change.
Are there any contentious BIPs, that could force another block-size type war?
I believe that we do need a hard fork to increase the block capacity at some point, I don't know if it will lead to another long drama though.
Please don't reply "the biggest event will be btc mooning/hitting 100k",
Well that is also one of the big events. The target is also $1 million in 5 years, not $100k. Also price is a good indicator for adoption.