Do you think RF shielding is necessary? Both Hackrf and Bladerf have it. Is it possible to limesdr?
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The HackRF has a 4 layer PCB (the GSG original does not have a shield installed, Nooelec sell a kit that you can install yourself). https://github.com/fd0/hackrf-one-pictures/blob/master/img_0008.jpg And having it installed does help attenuate external RF sources, but not so much with the self generated.
The BladeRF has an 8 layer PCB and it does indeed have a metal shield over most of the analogue front end. And it has exactly the same FPGA chip as the LimeSDR USB, well the BladeRF x40 does, it also has the EP4CE40F23C8N.
Looking at the individual gerber files for the LimeSDR it has a 12 layer PCB, and at most 7 ground planes between the top of the board and the clock plane, at layer 10 on the analogue side of the board. The greatest source of local noise would be from the clocks and they are further away and more shielded than on most of the other boards. I would guess that an external metal box would provide all that most people would require in terms of attenuation of unwanted external signals.
If you look at the LimeSDR it does look like you could add a shield over the entire analogue side of the board.
It is just that it also would cover the 10 U.FL connectors as well. But you would still have access to the external reference clock in U.FL on the digital side of the board 
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