The Nintendo eShop will not be available just before the system update hits according to a news bite on the European version of the store. It also mentions that new features will be available once the update is performed and players return to the eShop.

The message reads:

Dear customer,

On account of the upcoming system update, which will be available by 8 December, Nintendo eShop will be unavailable for a limited period while the main server undergoes essential maintenance.

Once work on the server has been completed and you have performed the update on your Nintendo 3DS system, you will be able to visit Nintendo eShop as usual and take advantage of the new features. A SpotPass notification summarising all the improvements to Nintendo eShop will be sent out soon.

Nintendo eShop team

It is uncertain exactly when the new system update will hit.