As the time will pass, the bitcoin will almost sure loose his no.1 position - i see no potential but inevitable truth in this. Tthe reasons:
- Bitcoin has a quite big problem not in scalability, but in all the progress and development - it is realloy slow comparing to other cryptocurrencies
- technology that Bitcoin use is old. and i mean, really old - there are plenty of better cryptos in technological meaning
- also, the PoW will be obsolete in near future - there is really big problem with the power/electricity that is spend on PoW coins, and as we see the old energetic industry falling down and green alternatives rising up

If I see some coin as the successor of BTC? Well, at this time the ETH has in my opinion still the best chance if this process will be slow. But there can definitelly be someone else that will come (maybe it exists right now, maybe not yet) and people will think it is the “overnight success”. No it wont be, it will take probably months or years, only difference will be when will people notice that crypto :)

btw: the argument, that it has the “firstcomer” place, is wrong. at first, Bitcoin was not first cryptocurrency, it is first that gain some countable atention from geeks and also part of the public, but is was definitelly not first. second - there was many times someone “first” in the market, who lost his status. one example for all -> MySpace vs Facebook. hardly anyone predict in the times of myspace kingship, that it will lose its status in few years. look at it now. and there are plenty of other examples - Yahoo vs Google, Nokia vs Apple etc