The cryptocurrencies role as a mediums of exchange can dramatically increase during a major fiat crisis. Although Bitcoin vastly outperforms other cryptocurrencies as a store of value, it competes closely with Litecoin as a medium of exchange and Litecoin will probably not stay the only one... I bet that while the cryptocurrencies role can remarkable increase the share of the first cryptocurrency among other cryptocurrencies become smaller.

Lightning cannot reach mass adoption. The architecture is just not allowing convenient use, because of liquidity and connection issues.

Bitcoin can power all online transactions theoretically using Ark, but probably requires covenants to be included in a future softfork. Ark is already working without covenants though, although it's debatable if that alone can power all online transactions.

I believe in the long run, Bitcoin may be used for all online transactions, but I don't believe so for the next few years. It needs something on top of it since the base layer does only about 7 transactions per second. Lightning seems like the obvious solution, but in my experience the problem of liquidity and routing still makes it unpleasant for daily users and @BlackHatCoiner has a point there. I like the idea of Ark but I'm not sure it can scale at this point.

Volatility is another problem. Only a few users would want to spend money that can go up/down by 5-10% in a single week, so most of the day-to-day crypto transactions currently utilise stablecoins. Bitcoin will likely keep growing in importance as a store of value and settlement layer and potentially as a payment mechanism as well.

The next few years are already by the corner and adoption is still very slow, from a quick search, less than 4% of the world population owns bitcoin and since fewer than 1% uses it for transactions, it shows the rest of the less than 4% are just buying and accumulating bitcoin, including myself. So my answer to this question is NO. The figures of adoption/transactions involving bitcoin should increase and a medium of faster payment like LN reach a bigger adoption before we can think of a "massive chunk"

The problem is that in a good number of countries, bitcoin is illegal and in others, there is unclear regulations towards it, thereby obstructing its efficient use for transactions within countries, a lot of people use it across countries though, starting from campaign managers here who pay for signature campaigns in bitcoin and casinos that accept bitcoin deposits and process its withdrawals, to other services that accept bitcoin payments.
If bitcoin can achieve good intra-country transactional relevance in countries it is legal, then we have a good starting point to proper globalization.

In my personal assessment, if Bitcoin still relies on its main network, namely blockchain, it can be seen realistically that of course Bitcoin cannot be one of the reasons for supporting all online transactions globally, What's more, in the near future, I think Bitcoin will still prioritize the concept of the Bitcoin main network, of course it will still prioritize security and decentralization as in the beginning.

Another reason Bitcoin cannot support all transactions, is because Bitcoin is still tied to block size and transaction fees such as gas fees, in blocks of 1 MB every 10 minutes, meaning that if Bitcoin is used for all transactions, transactions will automatically queue. jammed piled up, When a situation like this occurs Bitcoin users will pay expensive transaction fees so that their transactions run smoothly, of course it is not practical and realistic to buy a cup of coffee which should pay $1. When this situation occurs users have to pay up to $5 for a cup of coffee, right? that's not realistic.

The possibilities are there already, because in prop firms it's acceptable as means of payment, which is definitely an online transaction. This is just us trying to forecast the future of bitcoin which I think it's not easy, but I really think it has the tendency to power online transactions, but right now most people sees it as a form of investment rather than a means of exchange. We really don't know what tomorrow brings, so will not be surprised if it becomes a means for all online transaction in the future,  because bitcoin has been here for a very long time and it's already proven that it can be trusted when it comes to long term investment.

This is where lightning comes in. Bitcoin lightning takes seconds to send transaction across different channel. The lightning is even faster, like super faster than any of the layer transactions because even if it's congested, it doesn't wait for confirmation until there is settlements on the main chain which can be done when you want to close the channel. Bitcoin lightning can solve the scalability most people are facing everyday but I don't know why they don't like lightning.

Like if you visit some of the centralized exchanges, they have lightning deposit. Binance even recommend it for their users because they are one of the largest channel on lightning. Some of the challenges we have on lightning is even because people are not using it. If people start to use lightning for large scale transactions, there will be enough liquidity for even institutional investors. Imagined an institution with $1b open channel, it transactions are going to easily routed.

How Bitcoin will be used in the future and how much it will be used in real life depends on the mindset of the users. Bitcoin is still being used for transactions, but on a small scale. I think that if Bitcoin becomes more valuable in the future, it will probably gain more fame as a store of value. The issue is not the transaction problem or fees, but the holding benefit. You can profit more from Bitcoin by investing than by actual transactions, so people will choose the profitable option. If it is profitable for someone to transact with Bitcoin, then they will use it for transactions. However, the use of fiat currency will never end, and if there is a fiat crisis, Bitcoin can play a role as an alternative.

If we talk about the future, the question of Bitcoin being able to power all online transactions can be answered by hypothetically yes.  Since we do not know the future path of bitcoin development, we can only assume something like the developer creating a Bitcoin layer where transactions can be instantly confirmed and can process billions of transactions in a second. think of it as a greatly improved Lightning Network.

I am optimistic about Bitcoin development, and I also welcome any form of Bitcoin layer development as long as it helps Bitcoin establish its dominance and greatly enhance its performance.

 We speaking about Bitcoin layer one then it can't
It handles way less than the world does in a second
Due to its intentionally created constrain
But potentially with layer two then yes
Though it would be an alternative method to Fiat at best imo.