We are looking to use the 'soft commit' feature in Solr4 to support near real time search for our production application on Heroku.
Yes, and yes. Solr4 will become the default in Websolr sometime in March/April 2014, but for now you have to log into the Websolr control panel to create your Solr4 instance... the addon won't do it itself. If you need help navigating, please fill out a ticket on http://help.websolr.com, and someone can help you.