If people still accept fiat-currency for bitcoin, it is not to late to get in.
If price is really important, i am sure that bitcoin will easily reach $1,000,000 each
but after that there becomes too many factors where the dollar collapses or hyper-inflates, or both
AND bitcoin become too scarce or too valuable or too useful to trade for fiats.
What will happen to altcoins?
Don't know.
My guess is that lots of coins will be used and then, something better than atomic swaps,
and then its, in effect, one currency with multiple chains