RUKI and hypothetical ks- > sk- metathesis in BS

Hello,

I've encountered a few Slavic words beginning in /x/. Some dictionaries
hypothesize about possible ks- > sk- (or vice versa) metatheses. Can
somebody possibly help me? What are the pros and cons? Thanks for any help
or comments.

Best,

Pet'usek

P.S.: e.g. *xyba (error, mistake)