What "IF" no D300 replacement? What next?

There is still a lot of life left in my D300s. It's hard to know what kind of cameras will be around in about 2-3 years from now. If Nikon decides to let the semi pro DX line die, I'll probably switch brands, maybe mirror less Fuji X pro 'whatever', they make great lenses. I won't go FX, too heavy/big, expensive. Not sure if I could do nature and action photography the way I do it now with the Fuji system. A D400 would be the 'logical' upgrade to the D300/s and not the 'half @rsed' D6oo. It is a different photographic platform. Shooting The D800 in DX mode must be like driving a Mac Laren stuck in 2. gear on a goat track (I am only guessing of course). I am not worried about camera bodies (there are plenty of good cameras around). It's the lenses which give me 'pain' and pangs of desire. Cheers, Hans

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Hans