Even if an entity does not support SegWit they may prepare for SegWit in the event that it becomes part of Bitcoin despite their wishes.
Segwit is backwards compatible. If you don't like segwit, you can continue to use Bitcoin as you do now with almost zero impact on you.
There are now two transaction formats - legacy and segwit.
A node that doesn't support segwit will receive transactions in the legacy format. These transactions will not have the witness data, thus no signatures or public keys. This works because the witness program allows anybody to spend the output. A node that supports segwit will not accept a legacy transaction that attempts to spend an output using a witness program. Thus the need to get 95% of the miners to support segwit.
doesn't this mean you can't do a rescan any longer if you're stuck with old version after segwit, the old version doesn't know who is really allowed to spend the output?