"Yes. We're working on a plan for extensions for a future update to Project Spartan," tweeted the @IEDevChat team on Twitter.
There has been talk among various sources (including some of my own) that Microsoft is seeking ways to enable Google Chrome extensions to work on Spartan. All that the team said today was that they are "still building our plan for extensions."
Spartan is the replacement for both the Desktop and "Modern"/Windows Store versions of Internet Explorer. It will be able to run on Windows 10 Desktop and Mobile and will work with touch, keyboards and mice.
Spartan is not yet part of the Windows 10 Desktop preview builds. It also is not slated to be part of the first Windows 10 Mobile preview, due out in February. It will be added to both previews some time in the coming months, Microsoft officials said.
Update: Microsoft has only committed to bringing Spartan to Windows 10 so far, but the IE team said it will watch whether there's demand for it on Windows 7 and then decide what to do. I've heard the team could ultimately bring Spartan to some non-Windows platforms, but have no information on how or when that might happen.