Hello fakie,
I want to say a little more about this topic. Firstly I update AB right now with a couple of minor changes in the Camera control: now the "Quality" variable appear in the object inspector at designtime, and, I specify the JPEG as the encoding type for the captured image. Playing with the "Quality" variable and and the "TargetWidth" and "TargetWidth" ones, we may can get an smaller Base64 string to be uploaded, for example.
On the other hand, taking a look at the possible other results of the Camera's control, certainly they can give us the captured image's file URI, instead of their Base64 representation. The problem is what to do with that file URI... Certainly if we want to upload the captured image (not their Base64 representation) we must use another Cordova's plugin: the FileTransfer plugin, which is not included "out-of-the-box" in App Builder right now, but can be used like any other Cordova's plugin.
Maybe I can work in a FileTransfer included "out-of-the-box" in App Builder, but I can't promise nothing right now nor a time line. You can use it if you wanted right now, again, just like any other Cordova's plugin: using directly the plugin's Javascript API. However, and, said that, if we want a picture from the device's user, maybe we can achieve it without the usage of the Camera control.
We can use the Input File control (look at their "Accept" and "Capture" variables) in order to allow the user to get a picture from their device, and we can send the choosed image (not their Base64 representation) directly to our app's server, various samples shown how we can do it, like the "HttpClient" sample. This method has an additional advantage, and is that they work not only in Cordova's builded applications, but also in any modern browser. Take a look at the "ImagePick" and "ImagePick2" samples.
As an additional note, look at the "Camera", "Camera2", "Camera3" and "Camera4" samples. I just test right now the "Camera2" (for example) who take a picture from the camera and then upload the Base64 representation of the image: certainly they works acceptable in my device and with my internet connection: they take just a couple of seconds to upload the Base64 representation of the image. Then take a look at these samples if you are not take a look before!
Hope this information can help in some way!