I filed a bunch of Redmine related PRs in the past and some of them can be solved by bumping Redmine PORTREVISION after some of the dependencies rubygem are upgraded. 

Redmine has fixed version numbers dependencies, e.g.:

Today's upgrade:
        rubygem-thin: 1.7.0_1 -> 1.7.1
        rubygem-roadie: 3.2.1_1 -> 3.2.2
        rubygem-pkg-config: 1.2.0 -> 1.2.3
        rubygem-nokogiri: 1.7.2 -> 1.8.0
        rubygem-mail: 2.6.5,2 -> 2.6.6,2
        rubygem-jbuilder: 2.6.4 -> 2.7.0
        rubygem-bundler: 1.15.0 -> 1.15.1

Then Redmine cannot be restarted:

/usr/local/lib/ruby/gems/2.3/gems/bundler-1.15.1/lib/bundler/spec_set.rb:87:in `block in materialize': Could not find nokogiri-1.7.2 in any of the sources (Bundler::GemNotFound)

So I must use 'pkg upgrade -f redmine` to fix this issue.

Are there any mechanism in ports framework to watch these changes in dependencies version numbers and automatically bump PORTREVISION or at least notify port maintainer?

It is really annoying to have Redmine broken after each pkg upgrade and make upgrades thru Ansible very difficult task.