The Printstagram/Instagrid guy just released Dblcam last week for iOS. No video and it's not exactly simultaneous: snap rear-facing camera photo then immediately snap front-facing camera photo to produce a diptych. They've had the idea since "two years ago".
If that's two years of building then... I have no words.
Terrible execution of a great idea.
Reminds me of http://reactions.co/
Did they do it the way you wanted to? No. Things are missing. You're not satisfied. So create it. Don't worry about "copying". Welcome to the beautiful world of design. Filled with copying and iterations galore.
Design it. Ship it. Improve on it. Stop worrying about Samsung. Don't worry - because when/if they see yours it might just inspire them to "copy" and improve on theirs too.
This reminds me of the TechCrunch/Lyft/GigaOM fiasco in which a TC writer refused to write an article for Lyft after GigaOM broke the news of their launch first. So many people commented insisting that they didn't care if GigaOM broke it first, they wanted to read the TC take whether it came out five minutes or five days later.
There's such an emphasis on speed in this industry and often times I'm guilty of being impatient with product launches, but quality is just as if not more important. Also, your audience (iPhone users) aren't going anywhere. They're not going to switch to Samsung. Not to discredit the people at Samsung but I'm sure many people would be excited to adopt a well crafted iOS app like this and be willing to wait a little longer for said product.
Build it! Watching the Samsung keynote, they didn't sell me on this feature. You did.
Something that's important to recognise when you're working on products is that somebody else will almost always hit upon the same idea you're working on. You can either say, "Ah, well, they got there first" and give up, or you can say, "Ah, if somebody else is pursuing this, it's probably a good idea!" In this case, your concept has been validated. Users on iOS will be looking for an equivalent. Strike while the iron's hot!