Segwit (segregated witness) is a modern approach to address a couple of scaling issues of the bitcoin network.
Why Segwit would help with that?
The observation at the basis of Segwit is that inside the transaction data structure there are signatures data, this data is only used during a verification step (only one of the many operations inside a bitcoin node) but accounts to roughly 60% of the transaction structure. So segwit wants to give different weights to data inside a transaction and in particular move all the signatures to an "extended block" which will be used only for validation.
Why is the block size relevant to transactions throughput?
Because as of today inside a block of bitcoin blockchain there are indeed transactions data, so if block per seconds remains stable, the more transactions inside a block, the more the transaction throughput. Will it be a great increase? No but it prepares the foundation for a better organized data structure.
Is it solving issues / introducing other issues?
It is indeed solving a type of attack where transaction data can be re-written with other characters (transaction malleability bug) creating a new valid transaction that the attacker can broadcast to invalidate the real transaction. As any piece of new software it can indeed introduce unpredictable behaviors that can be exploited. The most interesting consequence is that the size of blockchain could scale out of what a normal consumer could store, making full validation of something centralized.
Will it have impact on miners?
Yes, transaction fees and validation time are predicted to grow apparently making mining less profitable. But don't forget that BTC price is dictated by the market so I am not much worried about it, miners are already mining against diminishing returns and the market rewarded them with rising prices. If the network stays healthy and is adopted in the industry there is no reason for the price not to follow accordingly.
Have other coins implemented it?
Yes, a list is maintained here: https://bitcointalk.org/index.php?topic=1777136.0
My point of view
Data-structure seems a simple problem but it is the basics of a good engineered system, if you ask me it is amazing that the malleability bug is not heavily exploited against currency exchanges and should be removed ASAP. Imagine you are an exchange and you cannot validate withdrawal transactions.. your users will be mad. Personally I am not bothered much by transactions per seconds as I believe bitcoin value is not in replacing payments networks.
Your point of view??
I am curious to see if savvy Steemians have an opinion on that! What do you think? Do you run a bitcoin node with segwit or without?