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Exactly. I mean, it's not that difficult to create a coin that would surpass Bitcoin in market cap and adoption. All its needs it's to implement SegWit at launch,
establish a very limited supply with no premine or ICO, and have active development to be able to surpass Bitcoin. By having a deflationary model and everything else just like Bitcoin, it would quickly gain traction. Especially by having SegWit within the first day of launch, which will be a huge booster for the new coin.
Also, there could exist a possibility of an existent altcoin to take over Bitcoin too. In my own opinion, both Ethereum and Dash look like the ideal candidates to become the top cryptocurrency in market cap. Just sharing my thoughts.

That will not work. The main reason that Bitcoin core does not want to increase the blocksize is that they want to force the "fee market" that is supposed to replace block rewards as the means of securing the Bitcoin network, while there is still enough of a block reward left to secure the Bitcoin network.
My take is that any proof of work coin that has a fixed maximum number of coins, with the exception of demurrage see edit 2, will not be able to scale unless it gives up de-centralization. In the top 10 coins Monero is the only proof of work coin that has given up on the maximum number of coins in exchange for a 0.6 XMR minimum per block reward in perpetuity. It is this minimum block reward that has allowed Monero to have an adaptive blocksize limit and thereby scale on the main chain without have to be concerned about the need for a "fee market" to replace block rewards.
I have not included Ethereum since it is planning to move away from proof of work to proof of authority or proof of stake. Interestingly Ethereum Classic moved away from a minimum block reward to a fixed maximum number of coins when the Ethereum Classic community decided to stay with proof of work. In my opinion this was a terrible mistake.
Having worked closely with the Monero adaptive blocksize, it has become very clear to me that
without a minimum block reward the Cryptonote adaptive blocksize limit will cause the total fees per block to go to zero at the same rate as the block reward. This will lead to no incentive for the miners to secure the Monero network. By analyzing the Monero adaptive blocksize and fee structure one can see why "solutions" such as Bitcoin unlimited will fail, since these type of solutions are in effect a much weaker version of what Monero already has. In the Bitcoin unlimited model for example net fees to the miner will fall to zero much faster than with a Cryptonote style quadratic penalty
Edit 1: Litecoin and Dash have fundamentally the same flaw as Bitcoin. In the case of Dash the situation is made even worse since the falling block reward not only has to support the miners but also the masternode network and project funding.
Edit 2: Demurrage as in Freicoin could be used to create a permanent block reward while maintaining a fixed number of coins.
I 100% agree with you.
In any case, this "limited number of coins" is more a religious thing than anything else, to boost speculation. A good currency has a mechanism built into it to regulate the value of the coin so that you don't have to check every day whether the sum that was going to buy you a car yesterday, is going to buy you a burger, or a house, tomorrow.
The problem with PoW is that even though it is not a bad idea to burn seigniorage, it is an awful idea as "cryptographic protection". One should have distinguished PoW for coin creation, and another cryptographic mechanism to decide upon the consensus, and eventually yet another mechanism to secure the consensus (immutability).
In fact, we can see the whole of crypto as a very interesting experiment on how some naive ideas lead to the consequences that have been predicted in some cases (like the deflationary spiral).