To make use of Segwit wallet software must upgrade to support it, that is a lot of work for Wallets Devs that generally are not getting paid for their work.
It is arriving as a soft fork to get round cores instances that hard forks cannot happen (even tho other cryptos have done it. Eth/XMR). The soft fork is not backwards compatible and bits exchanged by segwit will only be protected by segwit enabled nodes but in fairness with a 95% activation threshold that will be 95% of the network.
We have a number of mining pools now stating that they will not run segwit without a hard fork for a block size increase, the est hashrate is 10-15% that will refuse to run it, this will either mean core need to change their 95% requirement OR simply say no block size increase and no segwit.
Personally and sadly if bitcoin cannot grow past its current limits, I do not believe it will keep its first mover position.
Just seems insane that something that was marked as a global payment network is limited in its size. It is like limiting BGP routing tables to a size and saying "only certain people can play", and if you want to play, just pay more.
I'm not the person you replied to, but I can answer this.
Segwit is technically a soft fork, which means that it has some degree of backwards compatibility. Segwit will be redefining a previously-unused opcode in the bitcoin stack machine, which all old clients should treat as a NOP. So old clients will continue to operate normally with old transactions, but they will see segwit transactions as junk and be unable to validate them.
In the past this hasn't been much of a problem because soft forks have always implemented optional features. However this time it will be a problem, because the plan is to move all transactions over to Segwit. Any client that hasn't been upgraded once Segwit is activated will likely see no transactions at all, the same as if there had been a hard fork. So that's why they added a 95% activation threshold.
