The iPad will never be in trouble from any tablet except the iPad Mini. The general consumer will always want what they recognize most and they'll recognize the iPad before they recognize the Galaxy Tab this, Galaxy Note that, Galaxy Tab 4, Galaxy 10.1 Plus Extra, Galaxy Mega, Transformer, Nexus, Galaxy Nexus Tablet Plus 5, etc etc etc.
As long as the iPad is just the iPad, and the Samsung tablet is a bunch of random stuff, the iPad will do just fine.
Now if Samsung applies the S3->S4 strategy to tablets? We could see things get interesting. But they need features and and easy access approach which makes their tablet offering a better alternative than an iPad or at least the iPad Mini.
This is what I think Samsung SHOULD do if they want to challenge the iPad:
$250 Galaxy Note 8 - Offer the Note 8 at $250 but add flash to the camera and give it the S4's software. By doing this, you give people a no compromise alternative to the iPad Mini. (Sorry but the Nexus 7 sells decently but it doesn't sell 'iPad Mini' numbers because Google makes compromises with Nexus devices)
And if Apple wants to keep the iPad competitive, they need to add:
Flash to the camera
Follow through with the iPad Mini form factor
Give the iPad Mini comparable specs to the iPad 4 when the iPad 5 launches (Keep the mini one generation behind but not two full generations behind)
Centralize storage. One file for multiple apps. It shouldn't be hard for them to do this without giving users too much control over the OS.