P2PKH/Legacy address don't have place in future if bitcoin community move forward with newer technology, but surely it's slow process just like moving from IPv4 to IPv6
Also, i'm sure future technology/update won't support P2PKH/Legacy address. Even LN now drop support for P2PKH/Legacy address.
I think we will newer get rid of P2PKH legacy addresses. The network always has to be able to make transactions from them, because there will always be old addresses that have been made when the only choice was P2PKH.
Sometimes people find their OLD private keys. It would be strange if someone had "stolen" their money by disabling support for old addresses...
Also for security minded persons, legacy addresses may be better. They have been around longer, and haven't been cracked.
On the other hand, there are interesting articles about the security of SegWit addresses. (From the time when SegWit was coming.) If SegWit support is removed, then all coins in SegWit addresses would be "anyone can spend" -coins. And that would literally mean that
anyone can spend those coins!For big amounts of
BTC I will always prefer P2PKH addresses. For smaller sums, the spending wallet, SegWit wins.