Strida is a brand name. The manufacturer is Ming Cycles of Taiwan. The knock-offs are from mainland China from unknown manufacturer(s). Ming Cycles does continue to improve the Strida - many of the changes from 3.2 to 5.0 originated in-house there. They may currently be working on a hub design to accommodate a Schlumpf Speed-Drive for a future Strida model. This kind of innovation is driven by customer feedback, not the knock-off competition. I don't see anything new being developed by the knock-offs. The letter below is an example of Schlumpf and Ming Cycles collaboration:

Subject: Re: Can speed-drive be installed on Strida?
Date: Sun, 06 Jan 2008 23:10:03 +0100
From: schlumpf innovations <info>
To: Amuro Lee <amurolee>

Dear Amuro,

we sent a speed-drive to Strida and are waiting for their results. They told
me a few weeks ago, that they are working on a solution.

Best regards

Florian