I wouldn't be surprised if they don't. Valve don't want to sell hardware, they want to sell games. They only make hardware as flagships for new markets, then they want other hardware manufacturers to take over.
the legion go is more powerful and a has a nice screen, but is heavier, boxier, and has a worse batteyr life than the steam deck
They definitely are working on it. They announced the steam machine, steam controller, and the valve frame (standalone vr headset with seamless screen sharing from a PC), and in their reveal video the first thing they rather coyly say is “we’d love to share information about our next Steam deck, but that’s for another day!” and announce a bunch of other cool stuff.