It is still being considered and if you google it you can see what the responsible minister Ed Vaizey has said about that in the recent past. There are often parallels drawn with digital TV switchover, but that programme was completely different because the 800 MHz radio spectrum was needed for mobile phone networks. In contrast there is no obvious alternative use for the Band 2 frequencies and if the BBC were to switch off their national FM radio networks, the band would quite likely be used for more local and independent FM radio.
The main reason the BBC would like to turn off FM radio is that it is expensive to simulcast in both FM and DAB. The public take up of digital radio listening (DAB plus radio over digital TV plus internet radio) is about large enough and the proportion of cars with DAB is about high enough for the Government to consider announcing a switchover (I suspect switchover rather than switch off, as the former is seen as more of a good news story than the latter). But it seems to me that it is unclear that such an announcement would be particularly attractive and as it will inevitably take a couple of years or more and the next General Election is in 2020, it isn't obvious that either of the bigger parties would see this as a useful part of either a manifesto for the next Parliament or something to chalk up as an achievement in the current one.
But ultimately it could be wrapped up as part of a grand digital vision, including super fast broadband and 5G. There is a Digital Economy Bill in the drafting and maybe when that emerges, probably before the summer recess, we may hear more about FM/DAB switchover in the statements that emerge from Westminster. And the government is working on a "Digital Strategy" which also could conceivably bundle FM/DAB switchover as part of what DCMS is setting out to achieve. So we can't be sure, at least not by what has been said about this publically.
Anyway whatever is announced, it isn't going to happen overnight and personally I think that if you are attracted to the idea of buying a 2nd hand Naim tuner then you should do so because you will probably get loads of pleasure from it long before anyone actually switches FM off.