The release of NV is one thing, the DLCs are another. They may want to delay an announcement for 1, maybe even 2 months after NV is released, but DLC? DLC wont stop them. They can very easily hype up a DLC and hype up TES V at the same time.
People need to stop thinking every little thing is going to prevent Bethesda from announcing this game. They aren't a tiny little indie developer about to release their first game, this is Bethesda, and this is The Elder Scrolls. Some things, such as New Vegas, may very well delay their announcement, but little things, such as DLC for New Vegas, or the release of Popular Game A or B or C, will not matter nearly as much to them.