As previously covered on Examiner.com, The Flash was to guest-star in Arrow episodes 8, 9, and 20, in which the 20th episode would have lead to the character donning the red and yellow costume and serving as an origin story for his standsalone series.
According to Deadline Hollywood yesterday, plans have changed for the scarlet speedster.
After seeing actor Grant Gustin in the role of Barry Allen aka The Flash, executives decided that the character deserves his own traditional stand-alone pilot instead of an introduction through another series. So, Barry Allen will not donning the iconic costume in episode 20 of Arrow, he'll be wearing the costume in his own pilot instead. Currently, it is unclear what's going to happen to Episode 20 and whether or not there will be references to the character.
The change seems to be more of a timeline shift than any creative changes as the creative team of Greg Berlanti, Andrew Kreisberg, and Geoff Johns, remains the same.
It looks as though Time Warner wants the new The Flash series to run at full throttle from the very start.