What will happen to all those paper wallets in long storage if in the future core and others only support segwit?
If I go out in the garden in ten years and unearth my stash, how do I redeem it?
Not going to happen. You will always have a way of redeeming legacy addresses. Core takes backwards compatibility very seriously.
The alt market is here to stay - there is no putting the genie back into the bottle. But Bitcoin continues to have the strongest dev teams of all coins. That makes its incumbent position almost impossible to overcome with features such as Lightning, Rootstock, Schorr, Dandelion etc. And when the first Bitcoin ETF is announced, that will be the fuel-air bomb that sucks the oxygen from the alts bunker.