If success is defined simply by book sales, then I believe that 4E will be a success both this year and next.
From the WotC standpoint, success for 4E is not based on book sales alone (IMHO) but on the ability of this edition to change the business side of the RPG industry. That means for WotC to get off of the RPG financial rollercoaster of high cost production runs followed by long term sales to recover that cost and generate profit. The vehicle WotC has chosen to change the industry and provide them with greater financial stability and profitability is the DDI.
If WotC fails to attract (and maintain) the number of DDI subscribers they've forecasted, then 4E, no matter what the book sales, will be considered a failure.
From the WotC standpoint, success for 4E is not based on book sales alone (IMHO) but on the ability of this edition to change the business side of the RPG industry. That means for WotC to get off of the RPG financial rollercoaster of high cost production runs followed by long term sales to recover that cost and generate profit. The vehicle WotC has chosen to change the industry and provide them with greater financial stability and profitability is the DDI.
If WotC fails to attract (and maintain) the number of DDI subscribers they've forecasted, then 4E, no matter what the book sales, will be considered a failure.