Hi, our sites gets 32.632 requests having "BingPreview" in user agent string within 24 hours. Source IP address counts are distributed like this (only first three octets):

      7 40.77.176
   1300 40.77.177
   1320 40.77.178
   1271 40.77.179
   5088 65.55.210
    291 65.55.213
   4685 131.253.25
   5567 131.253.27
    711 157.55.12
   1665 157.55.2
   5798 199.30.24
   4929 199.30.25

In piwik/core/Tracker/VisitExcluded.php these ranges are defined:

            // Live/Bing/MSN
            '64.4.0.0/18',
            '65.52.0.0/14',
            '157.54.0.0/15',
            '157.56.0.0/14',
            '157.60.0.0/16',
            '207.46.0.0/16',
            '207.68.128.0/18',
            '207.68.192.0/20',
            '131.253.26.0/20',
            '131.253.24.0/20',

so it looks like Microsoft started to use new IP ranges, e.g. 199.30.16.0/20 a big one (DNS resolves these as "msnbot").

Are you interested in having the list in VisitExcluded.php up to date? Because Piwik also detect this bot by substring search in user agent string, so missing IP detection might not be a big deal...