Just a couple of points to add to this thread,
Mr Toad - Sumburgh has had a Cat 1 ILS for quite a while, long before the recent extention. It was reinstalled after the work was complete giving, as before, an ILS for Rwy27 and Localiser only approach for Rwy 09.
In that sense it has been an "all-weather" airfield for many years, but because we get all the weather at LSI there are of course some days when even the facilities there are not enough, be it can't-see-finger-in-front-of-face fog or wind at lots gusting lots more.
The cross runway 15/33 is a great help in daylight, unfortunately the prevailing wind is inconsiderately right between the two runways, but it is unavailable at night, effectively making Sumburgh a single runway airport during nighttime hours (of which there are quite a few this time of year.)
But what really are the options? Maybe we just have to accept that, in spite of our advances in technology in many areas, we can't put the brakes on ol' Mother Nature and sometimes have to admit defeat.
Shetland seagull's are among the hardest in the world, but some days even they take shelter and wait for things to improve.......