It would of course, at a large scale. If bitcoin would never scale, some other coins might take the spot who already has the lead in terms of adoption and development e.g. LTC or ETH. However, what coin would replace bitcoin that I have no clue about since I'm still wary about ETH rise and LTC seemed to be too far off the charts.
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.

if it was possible, it would have happened already!
nobody is stopping anybody from doing it and we all know code is open and you can just copy it and start a new coin with any specification.
the problem however is the adoption, nobody will give up bitcoin which has been around for a long time and trusted to go to a new thing.
and on top of that the developers these days are only looking for profit and their own pocket, they don't care about developing a good coin. so they never do it.