If Samsung shifts to Tizen and discontinues its Android lineup then Tizen will totally eclipse Android. Samsung is Android when it comes to market share and profitability. Samsung leaving Android will mean Android will cease to exist because no other company has the magnitude and marketing power as Samsung/Apple.
No they won't, Tizen has no ecosystem.
If Samsung actually did that, it would be the best gift that HTC, LG, ZTE, Sony, Motorola, and all the other Android phone makers ever got. Free marketshare, yay!
Remember Nokia? They were a titan in the phone industry. Where are they now? They backed the wrong horse...
To rebuff your point about Android = Samsung, LG alone could probably transition to take over Samsung's place in under a year, if the demand was there. LG isn't that much smaller than Samsung.
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This is a total waste of time and money, IMO. It's basically Samsung pretending it's Sony, coming up with its own proprietary system that they think they can push on consumers because of brand recognition. If they even thought of pulling the plug on their Android devices, they'd get a huge dose of reality.
More likely this will become just another product under the Samsung umbrella. Samsung makes Windows phones too. They may put marketing money behind Tizen at some point, and clearly they're trying to make it look as much like Touchwiz-equipped Android as possible, but come on, how stupid do they think consumers are? Microsoft thought they could do something similar with Windows RT -- hey look, it's a tablet that runs Windows!!! Oh wait, no apps - see ya later!