As a standard for HTTP/1.1 the browser can use 2 simultaneous connections to the server to do its requests. Currently a single threads seems to use just only one connections to the server. To make testing more realistic a thread / user should be able to use 2 simultaneous connections to retrieve objects. For the latest versions of Firefox it is even using up to 6 connections simultaneously. To make tests realistic, this woould definitly be a must. Especially for HTTPS it is more realistic because it involves SSL handshakes. Also many webservers are configured to hold a maximum of X connections, and when simultaneous connetions are used you would hit this twice as fast as when testing with only 1 connection (as JMeter does now).
We consider this feature very important, e.g. AJAX/GWT pages that execute commands in parralel cannot be now precisely simulated with JMeter. Commands that usually occur in conflicting times, JMeter executes sequentially.
First Requirement has been implemented as Concurrent Download. I will open a new Bug for second issue *** This bug has been marked as a duplicate of bug 50943 ***
This issue has been migrated to GitHub: https://github.com/apache/jmeter/issues/2275