I'm the developer of 8sms.
It seems that sms no longer works on the Nexus 7 3G if you upgrade to Android 4.4.
In the past, some people have been able to use sms on their tablets by downloading and installing a third party sms app (such as 8sms). Even though there is no stock messaging app with the ROM (and AFAIK, this is not an official feature), this has generally worked.
However, Android 4.4 KitKat on the Nexus 7 3G takes away this feature.
In Android 4.4, a messaging app must be set as the "default sms app" so it can be allowed to save new messages to the phone's message database. In other words, a messaging app must be the default sms app in order to operate fully.
In the Nexus 5 (and Android emulators), there is a setting Settings » ... » Wireless » Default sms app which allows you to choose your default sms app.
In the Nexus 7 3G, this setting DOES NOT EXIST.
(This is according to what one user of 8sms has told me. )
It seems that the "default sms app" is not supported on the Nexus 7. In other words, you cannot set an app to be the default sms app. That means it is not possible to use an sms app.
Can some other readers confirm this?
If confirmed, this is a LOSS OF FUNCTIONALITY.