The sentence "I wish I was" is correct and usable in written English. This sentence is used as a way to express a desire for something to be different than it is currently. For example: I wish I was taller so I could reach the top shelf.
"I wish I was.
I wish I was now".
I wish I was dead.
"God, I wish I was myself again.
"I wish I was three people.
I wish I was lucky like you".
"I wish I was invisible," Lance said.
I love the desktop app, it’s always running on my Mac. Ludwig is the best English buddy, it answers my 100 queries per day and stays cool.
Cristina Valenza
Retail Lead Linguist @ Apple Inc.