Probably ok for public filters but not ok for private filters imho, as it
may cause private filter stuff be known to those w/o access to it. Same
when a public filter becomes private later.

Possible solution. Make Special:Log/abusefilter visible only to users with the "abusefilter-modify" permission, the same we do with Special:Log/spamblacklist which is visible only to sysops.

Not a good idea. That would mean for public filters, the public won't have access to the modification logs.

A better solution would be to change Special:Log/abusefilter such that it would show change logs for public filters to everyone, and for private filters the change log is only shown to those who can see and modify the filter itself.

If that's possible that would work for me too. But what about private filters made public and public filters made private? I'd rather not undisclose edit summaries of formerly private filters to the whole public.

Currently, you leave comments in the Comments box; if you make a previously private filter public, its whole history (including the Comments) will become also public. So the issue you raise applies to status quo as well.