Agreed, and the RFE seems pretty popular as well.
If waiting for the next BES version & hoping it sorts this out is not an option for you, what I generally do is take a Policy Action each night to create a backup copy of the log file that I want to inspect, then have the Analysis inspect the backup copy. The Action just does something like dos copy /y c:\log.txt c:\log.bak. Not elegant, but it’s at least enough to check once daily that the previous night’s backup was successful.
Was and RFE ever created for being able to analyze a busy file with relevance? I am getting the “class fileIOerror” trying to run an analysis against a file.
Does “locked lines of file…” work for you?
In fact, we released a new inspector for this with v9.5.7 
locked line of <file>
References:
https://developer.bigfix.com/relevance/reference/file.html#locked-line-of-file-file-line
https://bigfix-wiki.hcltechsw.com/wikis/home?lang=en-us#!/wiki/BigFix%20Wiki/page/BigFix%209.5.7%20Release%20Notes
That is great! Thanks, that solved the issue.