Setting up a new site with 4.0: some extensions don't work

I’m trying to get a new site up and running with the latest release, the 4.0.

Using the blog 4.0 - using an old config section - seems to generate some issues I can’t understand. I will open a separate thread for this.

Similarly a plugin called middleman-meta-tags (from tiste) raise an exception saying that is no longer supported.
I can work around the latter, creating an helper in the config.rb file (though it would have been nice using something ready).

I’ve tried to use another gem, not specifically written for middleman. This is called meta-tags (https://github.com/kpumuk/meta-tags) and I can’t see any problem with this, but once referenced I get the following exception

Unknown Extension: meta-tags. Check the name and make sure you have referenced the extension's gem in your Gemfile. (RuntimeError)

Any idea?

probably they are changes in v4 API that those gems are not ready for. you should open issues there.