Nobody knows, and Sonos almost never reveal future plans, unless they involve 3rd parties, which this one does not.  Note this type of “add a pair of fronts and use the soundbar as a center speaker” request goes back a decade, and Sonos have never put out this feature,  It would appear that like every soundbar ever made, Sonos soundbars are not center speakers, they are soundbars. 

It would undermine their soundbars so I don’t think they are doing it.

In what way?  THe OP is asking for front left and front right in addition to a soundbar.

Let’s just go the whole hog … ha ha

It would reduce the Arc to a centre speaker while Sonos market it as a complete home cinema system.

I’m surprised that Sonos have not yet produced three separate ‘front channel’ speakers. Maybe with the left/right ones linked/powered by the center speaker to save on the need for too many cables.

And that would affect sales how?

A three channel AMP would be welcome.

I’d buy a three channel Amp and add speakers to it BUT ONLY if the center channel had an independent volume offset adjustment.

The three piece, all Sonos front unit makes sense too, lot of folks with big screens would appreciate the wider sound stage spacing the left and right speakers out to the sides of the TV would provide. Be nice for music stereo imaging too.

Maybe keep the very nice looking Arc design but split it into three parts. The issue would be making them independent units or slaves of the center unit.

Maybe a new center only unit (mini Arc looking) that would use other Sonos for the side speakers. Fives for the best music, 300s for the best Atmos or 100s for the least intrusive.