Q. Do I have to give up my right to publish 3.5 OGL products in order to publish 4e compatible products?
A. No. Publishers are free to print product lines under either the OGL or 4E GSL. We would love to see our industry colleagues convert their entire product offerings to 4E, as we are doing, but we do not expect or require entire companies to convert to the new edition.
See also: Sleazy proposed new Dungeons and Dragons license seeks to poison open gaming systems